Well, very nice gun. Your firing pin is busted. The markings are Mauser internal worker markings, just indicating that some part was checked or finished. Sadly no descriptions of those markings have survived.
The small distortion in the S/42 text is interesting. My 1937 S/42 has the exact same distortion which was probably the result of a broken or worn die.
What is the sequence letter on the frame below the serial number?
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