Tom, always glad to see a retired cop, I am retired Army MP
We'd need a lot more info to give you any good scoop.
Military sn's started at 1, went through 10,000, then started at 1a, 2a, etc., so a 4 digit was the MAX they had (I have only seen pictures of 10,000 serial numbered guns...
I would guess there was a crown N somewhere, because if it received a serial number it means that it was about to be accepted, so either stolen from the factory or it has been rubbed off.
Appraised? I assume, you are asking; is it worth a ton of money instead of a normal luger price? a shooter luger is worth $500-$600, depending on condition. A "normal" collector price is about $800-$1500, and can be more. If it is not marked on the top, such as DWM, then it could be one of the so-called "sneaks", a time period of transition from DWM to Mauser and you find toggles with no manufacturer info, OR it has a replaced toggle that was blank.
Look to your left and go to the tech area and print out the forum of what info we want. but if you can provide digital pictures, lots of pictures, both sides, top, etc, and we can help. If you are worried about the serial number being seen, blank out the last 2 or something, although that is a lot less of a risk than folks believe. If you need help in showing pictures, then email me with them digitally;
weimar_lugers@comcast.net
Ed