If there is a name and number on the gun, it may also be a case number. Back in the day it was not unusual for LEO to scribe the number on the slide. I should know, I got one back like that, after an investigation by a cop who didn't think citizens should have guns, even with licenses. He made sure I remembered him. I re-nickled the slide, upon the judges order that the pistol be returned to me.It was quite often done in NYC, even thought it was not an approved procedure.