It's a former NYPD service revolver. The second set of numbers on the butt is the shield number. And I'm going out on a limb here a bit, but I believe there is a bit of a pun here with the serial prefix. The shield number is quite low for 1947, but when a patrolman was promoted to sergeant, an S was added in front of a number. It almost looks like they utilized the S-prefix to make a sergeant's number. (To give proper credit, my "expertise" on this comes entirely from Robert Vivas' NYPD gun website )