RWTF,
Did you get any pictures you could show us?
Below are some pictures of my unmarked 12 gauge Fox that might look similar to the one you saw.
No markings at all on the sides of the receiver/frame, top of the barrels, barrel flats, water table or fore end iron and no serial number on the trigger guard.
It does have the typical markings of Krupp barrels on the bottom of the barrels just forward of the flats. It has 28 inch Mod and Full barrels.
Trigger guard is engraved with initials: "F?C" who I think might be Fred ? Coleman. He was a fairly well know live pigeon and trap shooter back in the 1910's.
A Fred Coleman is listed in the 1908 Philadelphia Directory as a gun maker and lived just a few blocks from the Fox factory. Fred Coleman is mentioned in Mike McIntosh's book on Fox shotguns.
It looks like a Fox early B12 but it has a couple added features: the rib that goes from the bottom of the barrels up to the top like a BH Parker, the unique checkered side panels that look somewhat like a trap or live bird field and the fancier checkered stock and fore end.
No SN or markings under the trigger guard, fore end iron or on the inside. I had a top notch side by side gun mechanic fix the SAFEty slide and look for markings. None.
The non auto SAFEty slide that when I got the gun, was very difficult to slide back to the SAFE position. Much better now.
Any thoughts from anyone?