Probably the easiest to find is "THE STANDARD DIRECTORY OF PROOF MARKS" by Gerhard Wirnsberger translated by R.A. Steindler. It takes a little study to understand the German section but then the other sections are more or less parallel.
Also you may be able to find The History of Proof Marks as printed over a couple editions of Gun Digest beginning in the 22d edition. Maybe someone on here would be willing to copy and mail a set of these too you. They are easier to understand than Wirnsberger I think.
Last edited by Jerry V Lape; 10/12/10 04:09 PM.
