I found the following proof marks on the back side of a pair of percussion locks. The locks were sold at Bowlby & Brenner Hardware in Philadelphia. I know this from the marks behind the hammers. These 2 new marks were found when I pulled the locks for some clues. Both locks have the same proof marks on the back side of the hammers. These are "3 Pin Locks" and I am told they are American made.
Thank you for any help.