I’ve had a couple of those in the past, I remember that they were watchclock keys. A watchman would find them chained to a receptacle at a station on his tour and would have to put them into his watchclock where they would cause a paper disc to be stamped with the station, date and time. The particular location of the piece extending from the side caused the marking. I never knew the brand of the clock associated with those keys.
Antoher famous watchclock company was Detex but their keys were significantly different as they had an L shaped bit with a raised number on the end of the bit. I think I still have one of their keys somewhere.
BBE.
