All Tag Heuer watches have serial numbers located on the back of the watch case that distinguish a real watch from a fake one. A real Tag Heuer watch has two numbers on the back, one on top of the other. The bottom number is the serial number
Tag Heuer serial numbers typically have two letters and four numbers with some exceptions. A certified chronometer watch has six numbers without letters. Some serial numbers may have three letters and three numbers. All serial numbers are unique to the watch and contain six digits. Tag Heuer watches can be registered on the Tag Heuer website using the customer information and serial number to determine authenticity.