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

https://www.bookmarkmaster.win/if-you-re-checking-what-your-rolex-is-worth-before-selling-or-borrowing-against

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.