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

https://www.fastbookmarks.win/if-you-re-in-san-diego-and-considering-a-loan-on-your-rolex-ask-for-the-rate

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.