I don’t know anything about the maker but the gauge is clearly a mortising gauge that should have two pins, one of which would slide back and forth in the slot and moved by the screw on the end. The mechanism can be a bit delicate and sometimes the pins can break off. It might be that someone, not knowing the tool, cranked the movable pin against the fence wear plate and snapped it off. Make sure the fence is loose when you try to work the screw because locking down the fence will typically lock down the sliding mechanism. It should still be useful as a simple marking gauge or you can attempt to replace the missing pin and/or freeing the screw mechanism by taking the screws out of the brass wear plate on the arm and accessing the internal mechanism. Restoration would require a little metal working but would probably be worth the effort. Keep the screws from the wear plate in order if you do take it apart because some of the old screws are not standard and the screw holes were matched to the screws. You want to make sure that the screws don’t interfere with the wear plates or the fence.
Nice find. Have fun.