It would be interesting to see a photo of the stein.
That mark does not look like a stein mark. It looks like a silversmith’s mark. It resembles the mark of the city of Freiberg, a city in southeast Germany near Dresden that has been famous for silver since long before steins were made.
So my suggestion is to try to look up silversmith’s marks, especially if you can find them from Freiberg. It may have been one of the silversmiths from there.