Citizen serial numbers are typically found on the case back, often engraved or stamped into the metal. The serial number format has varied over the decades, but many Citizen watches use a numeric serial that can sometimes be decoded to indicate the production date. On some vintage models, the first two digits of the serial number are often associated with the production year, though this convention is not universally consistent across all product lines.
Modern Citizen watches, particularly those in the Eco-Drive line, may use alphanumeric serial numbers that follow a different coding system. The serial number is often accompanied by a caliber number (typically starting with a letter followed by digits, such as 'E111' or 'H500'), which identifies the specific movement used in the watch. Cross-referencing the caliber with Citizen's technical documentation can often provide additional context about the watch's features and production era.
It is worth noting that Citizen has operated multiple factories and produced watches for various markets under different sub-brands and labels, which can complicate the serial number decoding process. Collector communities and dedicated databases can sometimes provide assistance with unusual serial number formats. For definitive production date information, contacting Citizen's customer service with the serial and caliber numbers is commonly recommended.