Wood Grip Markings
 

Hi All!
I just purchased my first Luger today, so excited to be joining the ranks of owners. I've been searching the forum high and low but can't seem to find the answer so hoping you can help.

I purchased a 1939 marked 42 Luger, SN 8573q. I've fully disassembled the gun and it is all matching but the grips have me stumped. They're the wood grips, but on the inside of the grips there's no serial number, or proof marks. The left grip has the capital letter "R" stamped three times, the right grip has the capital letter "S". Does this mean they're replacement grips? I'd heard mention that sometimes letters were used but couldn't find much info. Pictures are attached. Thanks in advance!

Usually most have the last two numerals and I would guess the are an inspection mark~ Just a guess! Eric