Markings on frame underneath grips
 

Hi,

When I took the grips off the M11, I discovered some letter markings, on several parts of the frame. These markings are normally invisible as they are covered by the wood grip. They are a bunch of random letters. K and V on the left and right side of the fastening screw. Letter A just besides the grip safety.

Anyone have an explanation for these markings?
The Dutch Luger book doesn't mention them.