Could that not be the initials of the "repairer" indented into the lead? If so, they're upside down in the last pic, and may be "D F".

Great video, Stephen. Thanks for sharing that. Interesting to finally learn the correct pronunciation of Fanzoj. I wish more Americans would learn how to pronounce Leupold, the great American 'scope company. (It's Loo - pold, not Lee - uh - pold)

May God bless America and those who defend her.