For sixty-four years, a brass key has hung on a nail beside the register at Pegg’s Hardware, labeled with a paper tag reading only “?”. No one knows what it opens. This week, the store made a copy.

“It just felt irresponsible, having only the one,” said owner Rusty Pegg III, whose grandfather first found the key in a drawer of the store he bought in 1962. “What if we lose it, and then we find the thing it opens? Where does that leave us?”

Over the decades the key has been tried in every lock in the municipal building, both churches, the bandstand storage box and, during one memorable weekend in 1998, every padlock at the marina. It has opened nothing. Its teeth suggest a cabinet, experts say, though they concede “experts” is a strong word for people who are simply also curious.

The copy hangs on a second nail, with a tag reading “? (BACKUP)”.

“Some towns have a mystery lighthouse, some have a ghost,” Mr. Pegg said. “We have a key. I think it shows a certain modesty.”