The usual procedure for the engraving of NYC PD "Trophy" guns was for a local engraver over in the jewelry area of Canal Street and the Bowery do it while the job was being waited for.
Of course legally it was wrong, as NONE of the engravers was a Licensed
Gunsmith. ( NYCPD Regulations specifically listed engraving of guns requiring a Gunsmith License.)
Many earlier NYC PD "Trophy" guns were USED guns obtained from the Property Clerk. A dear friends was a .32 Pocket Positive, which he still has these 60 some odd years later.