Tough call. If you blow the pic up, the number and letter stamps appear to be over the swirl marks, which could have been created by anything from a sanding disc to an abrasive pad used for cleaning the pad, but who knows. Font looks decent, but the pattern of marking is a little unsettling. People do some strange things to block pads - these marks look pretty fresh. Would have been safer to have left it alone, in my opinion.
Regards,
Steve