Looks to me as though it was put on using a sharpie. Bet it comes off with acetone. It was not put on there by Omega. The watch may have been owned by a collector who attended a a “stare and compare” event with other collectors, and that was his ID.
The watch was purchased new directly from an Omega Boutique
That wasn't bought recently, was it? Looks like the back of those lugs have been polished (the serial number isn't crisp and sharp like they come from the factory). I wonder if the watch had some repair work done and that is a service mark.