It's a night watchman's key for use with the Detex watch clock system. Each station on a watchman's route has a box containing a key. When the station has been checked, the watchman inserts the key into the clock that he carries. When the key is turned, the number on the key bit is imprinted onto a paper disk inside the clock, recording the station number, hour, minute, day month, and year.
Correct. They were also used in the Navy for sound and security watches. The number on the key made an impression on a tape inside the clock, therefore proving what time that particular area was checked. Hated those 4 hour watches. Art...