The question still remains as to "IF" it was infact a proof mark. It is found in no list of marks I have access to, including Wirnsberger, Kennet, Englehardt, Greener's 1910 edition etc & seems to be on few if any guns of makers other than J P Sauer, which leads one to think it is some sort of proprietery stamp & not a proof mark. "IF" it is indeed a proof mark what proof does it indicate?? We have reference to what all the others are for.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra