velodog455~ is correct the marks are from an end mill machining process.
Luger's that have them have not gone through the final finishing stage ... this was due to war time manufacturing where the finish of the gun was less important than getting the gun to the soldiers @ the front.
I have never seen these milling marks on commercial Luger's but its possible.
As for your 'addiction' just be thankful you aren't addicted to collecting teaspoons or beer cans etc,
