Help with info re: BYF 1939 Luger with unusual marking

[kro]

After telling a friend about the help that was given me on this forum he asked that I post some pics of this Luger to find some information about it. The questions are regarding two things in particular. First is the year and BYF code. Isn't a 1939 chamber date and BYF code unusual? Second was is the significance of the little marking that is on the bottom of the stock lug and on the magazine base. You can see the symbol on the stock lug in pictures 6 & 7 and on the magazine in pictures 7 & 8. All numbers on every part on the gun match. Any help and comments would be greatly appreciated.