Please Help Identify Unit Marking on 1916 DWM

[Don M]

Bruce, this pistol once had a sear safety that has been removed. In addition, the side plate has been replaced and stamped with a matching serial number. The clue is the hole in the receiver flange just above where the main safety contacts it. This is where the rivet attached the sear safety spring. I had to lighten your photo to show this clearly.

There is the remote possibility that the gun was drilled for a sear safety that was never installed. One way to tell is to remove the side plate and see if there is a vertical hole drilled in the sear bar. If there is, the sear safety was once installed and the side plate is a replacement. If it were the original, it would have a slot cut out of the top.