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

https://super-wiki.win/index.php/Is_It_Smart_to_Sell_a_Rolex_If_You_Think_It_Might_Keep_Appreciating%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.