The NPF is Austrian Ferlach smokeless proof.
Ferlach was the heart of the Austrian gun guild country and small makers there turned out a lot of guns with no brand name.
1992.38 apparently means the 1992nd gun made and proofed in Ferlach in 1938.
I don't know about all those numbers on the bottom rib. Maybe the maker's serial number and ID code are in there somewhere. Can you pick out a number in the format shown at:
http://www.shotguns.se/html/austrian_trademarks.html