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

https://johnathanrcpw248.wpsuo.com/what-counts-as-a-complete-set-for-a-rolex-sale

If you’re checking a Rolex in San Diego, the reference number is engraved between the lugs at 12 o’clock, beneath the bracelet. Don’t pry the bracelet off yourself. Ask a watchmaker to check it before you sell or borrow against the watch.