That looks familiar to me. I am thinking it went on a belt and was used to hold something. I think the loop might be bent as it would have hung straight down from the frame so the hook would have held the item better. Is that clear as mud to you?
Yep, attached to standard leather work belts - not the really large contractor-style belts with pockets, but about the largest width belt that will fit in the loops of a pair of jeans.
Could hand a screwdriver or any other tool that had a hole in or loop on the handle. Hadn't seen one of those in....well, never mind!