Rolex watches have a serial number unique to the watch, in addition to a case reference number also unique to the particular model. Both are engraved upon the watch itself.
The location of the serial number on the watch depends upon the year of the model's manufacture. Before 2005, Rolex engraved both kinds of numbers on the side of the case in between the lugs that fasten the straps to the watch case. Since 2005, Rolex has engraved the serial number along the inner edge of the case beneath the bezel, beginning at the 6 o'clock position. The location of the case reference number has not changed.