Vintage Flushmount Backup/Tag Light with Clear Lens

Lens and chrome shows signs of use and wear. Wire and socket guts are missing. Minimal rust on fixture and socket bracket. 

It fits 1-3/4" hole. Metal prongs look good. Found this in my dad's shed, but I can't find anything listed like this, so I'm not sure if it is a backup light, tag light or some other kind of marking light. If anyone recognizes it, please let me know so that I can list it properly.