Re: Need help to identify old german 12 gauge shotgun
As far as I can tell, the name Illix Aind, Berlin, is on the gun and that should be good enough for identification and registration. The first name is unusual but not unknown in Germany and France.
I can't make out the other markings, maybe a better picture would help or maybe you can tell what some of it is and we can help.
FWIW, the crowned letters are S for proof of a smoothbore barrel, W for proof of a choked barrel, and U for the final definitive proof, per the German proof law of 1891.
The style of the gun indicates manufacture in the late 1890's or early 1900's.