Bruce, you have a fascinating and enigmatic Luger that I would pay $1K for any day of the year! (You must temper this with the fact that I am mainly interested in German police markings over the condition of the gun.) Prior to yours, only eleven examples of this marking were known to me. Unfortunately, the meaning of the marking remains unknown. These markings are discussed in
History Writ in Steel, pp. 322-324). Since this is your first Luger, you probably don't have a copy of the book but you can get some information from item 5 on this web page:
http://www.historywritinsteel.com/New_Insights.html.
The notches on the gun are unique and may offer some clue as to the meaning of the marking but at the moment, I can't figure out what they mean. I know there are folks who will jump to the conclusion that these are from a concentration camp (
Konzentrationslager) and the notches indicate the number of prisoners shot but I am not ready to endorse that.
I would greatly appreciate having your permission to use your photo of the grip strap in a future publication. If you agree and send me your name to the email address below, I will certainly credit you.
Thanks for posting this unique example. It has my curiosity about these markings aroused again!