Denny is about on the mark. I have an Ac 42 #3019 with this mark. I have not forund this in print form but another collector had told me this mark was for Beschuss Zella Mehlis. Your flare pistol is correct.That was the reason I ended up with mine figured it was a bit more odd than others I had seen.Wolfgang Kern is the guru on german flare pistols here is his site. At some point I'll get a book or two of his. But 6 flare guns does not a collector(thats me!!) make.
Bret