The picture is of the lock mortise in the door of a 100 yr old tall clock. The silver "thing" on the right is a piece of wire stuck into the right side of the mortise at the lower end and free at the upper end. It seems to exert no tension; i.e., it can be bent flat against the side of the mortice easily and will not spring back. It is probably away from the wall only because I was probing to see what it might be. It also appears to be independent of the lock mechanism, which does not have any indentations or tabs to engage the wire. 

Any ideas other than a stray piece of wire that got trapped during assembly? 

A shim of sorts to tighten the far end of the lock in the mortise?

Tom, the wire does not go through the side. Unless the hole is so tiny that I can't see it, it doesn't look like it was driven through from the outside.

Bill, it's possible, but why use a very thin wire rather than a piece of shim stock?

Dana, no, it's not a nail. Very thin wire.