I know of two marked Neumann Bros.
12ga sxs, 30inch steel, greener bolt. Two antelope on left lock plate.two ducks on right, marked Neumann Bros.
Barrels have the SPI mark (a co-op of Jansen, Doumoulin,& Neumann- Translates-sorta- to Society Pieces Interchangable) Very well made, proper barrel flats, not a JABC!
also:
A 410 sxs, 24 damascus, fully scaled, very, very cute.
Also marked Neumann Bros, and Machine Made. Some engraving, no animals etc.
Butt plate is missing, so no info on that.

Dumb, but learning...Prof Em, BSc(ME), CAE (FYI)