Longines case backs typically feature the famous winged hourglass logo, which is one of the oldest registered trademarks still in active use. The style and rendering of this logo have evolved over the brand's nearly two centuries of production, and the specific version can sometimes help approximate the era of manufacture. Vintage Longines case backs often include additional markings such as the case material, case maker's marks, and sometimes the Longines name in period-appropriate typography.
On vintage Longines watches, the case back may display hallmarks indicating the metal type and purity, particularly for precious metal cases. These hallmarks can sometimes provide dating clues based on the hallmarking systems of the relevant country. The case reference number, when present, can help identify the model, though vintage Longines case numbering is generally less standardized than modern systems.
Modern Longines case backs are more standardized and typically display the winged hourglass logo, the Longines name, the model reference number, caliber designation, water resistance rating, case material, and 'SWISS MADE' inscription. Many current models feature exhibition case backs with a sapphire crystal window. Some special editions and heritage models carry commemorative engravings or designs on the case back. As with all fine watches, case back markings should be verified alongside the movement and dial for comprehensive authentication.