Seiko is a Japanese watchmaker founded in 1881, renowned for producing a vast range of timepieces from affordable quartz models to high-end mechanical watches. The brand is known for its proprietary movements and vertically integrated manufacturing. Seiko watches typically carry a variety of markings on the case back, dial, and movement that can help identify the model, caliber, and approximate production date. Understanding these markings is often essential for collectors seeking to authenticate and date vintage Seiko pieces.
Seiko Watch Markings & Identification Guide
Seiko watches
Common Models
Seiko 5Seiko PresageSeiko Prospex (SKX series)Seiko Turtle (SRP series)Grand SeikoSeiko King Turtle
Serial Number Information
Seiko serial numbers are typically found engraved on the case back of the watch and often follow a six-digit format on vintage models. The first digit commonly indicates the production year, while the second digit is often associated with the production month (where 1-9 represent January through September, and O, N, D are sometimes used for October, November, and December). However, this system can vary by production era, and some references suggest that the month coding changed over different decades.
Because the year digit is a single number, the serial number alone typically cannot distinguish between decades. For example, a serial beginning with '8' could potentially indicate 1968, 1978, 1988, or 1998. Collectors often cross-reference the serial number with the movement caliber, case style, and dial characteristics to narrow down the production decade. It is worth noting that Grand Seiko models may follow a different serial number convention, particularly newer references produced after the brand's relaunch as a separate entity.
Some modern Seiko watches, especially those produced for international markets, may use longer serial number formats or different coding systems. Always consider that serial number formats can vary by factory, production line, and era. When in doubt, consulting Seiko's official service centers or reputable collector communities is commonly recommended for accurate dating.
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What to Check Next
Common Markings Found on Seiko Watches
Serial Number Engraving
A unique alphanumeric code engraved on the case back that identifies your individual watch. This number is typically used for warranty registration, service history, and authentication.
Model Number StampAn alphanumeric code stamped on the case back that identifies the specific watch model or product line. This number is essential for ordering replacement parts and identifying your watch's specifications.
Water Resistance Rating (Case Back)A marking indicating the watch's tested water resistance depth, typically shown in meters, feet, bar, or ATM. This rating describes laboratory test conditions, not actual diving depth recommendations.
Case Material MarkingAn engraving or stamp indicating the material the watch case is made from, such as stainless steel, titanium, or gold. This marking helps verify authenticity and informs care and maintenance decisions.
Crystal Press Back SymbolA small symbol on the case back indicating it should be opened with a crystal press tool rather than unscrewed. This marking guides watchmakers on the correct method for case back removal.
Japan Movement StampA case back marking indicating the watch uses a movement manufactured in Japan. This is commonly seen as "JAPAN MOVT" or "JAPAN MOVEMENT" and denotes the origin of the caliber inside.
Stainless Steel Back StampA marking reading "STAINLESS STEEL BACK" or "ST. STEEL BACK" indicating the case back material. This is commonly found on watches where only the back is stainless steel while the case body may be a different material.
Clasp Code StampAn alphanumeric code stamped on the bracelet clasp identifying the clasp model and sometimes the production date. This code helps identify replacement clasps and can aid in dating the bracelet.
Bracelet End Link NumberA number stamped on the end links of a bracelet identifying their specific shape and size. This number is critical for finding replacement end links that properly fit your watch case.
Bracelet Model NumberA unique identifier stamped on the bracelet that specifies the exact bracelet model. This number is essential for ordering correct replacement bracelets or links.
Adjustable Clasp IndicatorMarkings or features on a clasp indicating it has micro-adjustment or on-the-fly sizing capability. This allows fine-tuning of bracelet fit without tools.
Case Reference NumberA manufacturer-assigned reference number identifying the specific watch case design, dimensions, and material. This is the primary identifier for sourcing correct case parts and compatible accessories.
Lug Width MarkingA number stamped between or on the lugs indicating the distance between them in millimeters. This measurement determines which strap or bracelet width fits your watch.
Bezel Insert CodeA code identifying the specific bezel insert installed on a watch, typically relevant for dive watches and GMT models. This number is essential for sourcing correct replacement inserts.
Crown Logo StampA brand logo or emblem stamped or engraved on the watch crown. This identifies the manufacturer and can indicate whether the crown is an original or replacement part.
Case Size IndicatorA marking indicating the watch case diameter or dimensions, typically in millimeters. This helps identify the watch model variant and determine strap compatibility.
Caliber NumberA manufacturer's identifier for the specific movement (mechanism) inside the watch. This number reveals the movement type, features, accuracy, and service requirements.
Jewel Count MarkingA marking indicating the number of jewels (synthetic rubies) used as bearings in the movement. This number reflects movement complexity but is not a direct indicator of quality.
Movement Country of OriginA marking indicating where the watch movement was manufactured, such as "Swiss" or "Japan." This identifies the movement's origin, which often influences perceived quality and value.
Regulation MarkingMarkings on or near the movement's regulator indicating adjustment positions for timing accuracy. These are used by watchmakers to fine-tune the watch's rate.
Shock Protection SymbolA marking indicating the movement incorporates a shock protection system for the balance wheel. Common systems include Incabloc, Diashock, and Parashock.
WR 50M / 5 Bar MarkingA water resistance rating of 50 meters (5 bar/ATM), indicating the watch can handle everyday moisture like rain and hand washing. This rating is not suitable for swimming or submersion.
WR 100M / 10 Bar MarkingA water resistance rating of 100 meters (10 bar/ATM), generally considered suitable for swimming and recreational water activities. Not rated for scuba diving or high-impact water sports.
WR 200M / 20 Bar MarkingA water resistance rating of 200 meters (20 bar/ATM), suitable for serious water sports and recreational scuba diving. This is the standard entry-level rating for purpose-built dive watches.
Bar / ATM Pressure RatingA water resistance rating expressed in bar or ATM (atmospheres) instead of meters. One bar/ATM approximately equals 10 meters of water depth in testing pressure.
Japan Movt MarkingA case back marking indicating the watch uses a Japanese-manufactured movement. This is one of the most common markings found on affordable watches worldwide.
Made in Japan StampA marking indicating the watch was fully assembled in Japan, not just the movement. This designation is particularly valued on Seiko, Citizen, and Orient watches for the domestic Japanese market.
Kanji Case Back InscriptionJapanese characters (kanji or katakana) engraved or printed on the case back of watches sold in Japan. These inscriptions typically convey model names, material descriptions, or brand text written in Japanese.
JDM Model Reference CodeA model reference number specific to the Japanese domestic market that differs from the international version. JDM codes often follow unique formatting conventions, such as Seiko's alphanumeric SBDC or SARB prefixes.
PSC Diamond Safety MarkA small diamond-shaped symbol required on consumer products sold in Japan under the Product Safety of Consumer Products Act. On watches, it confirms compliance with Japanese electrical and safety standards.
Domestic Market Dial TextJapanese text printed on watch dials indicating features or specifications in the domestic language. Common examples include characters for water resistance, automatic winding, or material type on JDM-exclusive models.
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Frequently asked questions
Where can I find the serial number on my Seiko watch?
The serial number on a Seiko watch is typically engraved on the case back, often alongside the caliber and case reference numbers. On some models, you may need to remove the bracelet or strap to see the full engraving. Vintage models usually display a six-digit serial number, while newer models may use a different format.
How do I decode a Seiko serial number to find the production year?
The first digit of a traditional six-digit Seiko serial number often indicates the production year, and the second digit commonly represents the production month. However, since the year is a single digit, it can correspond to multiple decades. Cross-referencing the caliber number, model style, and other markings is typically necessary to determine the correct decade.
What does the number on the Seiko case back mean (e.g., 7S26-0010)?
This format typically represents the movement caliber followed by the case reference. In '7S26-0010', '7S26' commonly indicates the caliber (movement type), while '0010' refers to the specific case design. Together, they can often be used to identify the exact model and look up its specifications in Seiko catalogs or collector databases.
How can I tell if my Seiko watch is authentic?
Authenticating a Seiko often involves examining the case back markings for correct formatting, inspecting the movement for genuine Seiko construction, and verifying that the dial printing and logo are consistent with known examples from the same era. Because Seiko has produced an enormous range of models, consulting experienced collectors or a qualified watchmaker is commonly recommended for definitive authentication.
What is the difference between Seiko and Grand Seiko markings?
Grand Seiko watches typically carry distinct markings, including the 'GS' logo on the dial and the lion medallion on the case back. Their serial number formats and caliber designations often differ from standard Seiko models. Since Grand Seiko was relaunched as a more independent brand in 2017, newer models may follow different marking conventions than vintage Grand Seiko pieces.
What do the water resistance markings on my Seiko case back mean?
Seiko case backs commonly display water resistance ratings in either meters or bars. For example, 'WATER RESIST 10BAR' typically indicates water resistance to approximately 100 meters. However, water resistance can degrade over time as gaskets age, so the original rating may not reflect the watch's current capabilities. Regular pressure testing is often recommended.
What does the wave symbol (Tsunami logo) on old Seiko watches signify?
The wave or 'Tsunami' symbol found on some vintage Seiko case backs is often associated with the Suwa Seikosha factory and was commonly used during certain production eras. Its presence can sometimes help narrow down the production period or factory of origin. Collector communities maintain detailed references about which logo variants correspond to specific eras.
Can I determine the movement inside my Seiko watch without opening it?
In many cases, the caliber number printed on the case back can indicate which movement is inside the watch. However, it is possible for movements to have been swapped during servicing, so the case back marking alone is not always a guarantee. For definitive identification, having a qualified watchmaker open the case back is commonly recommended.
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