If you’re checking a Rolex in San Diego, the reference number is engraved...

https://source-wiki.win/index.php/Can_I_Get_My_Rolex_Evaluated_for_Free_in_San_Diego%3F

If you’re checking a Rolex in San Diego, the reference number is engraved between the lugs at 12 o’clock, under the bracelet. Have a watchmaker remove it rather than using a knife, and don’t post clear photos of the serial number.