What has been dubbed the "Hound of Hartlepool" has been unearthed by archaeologists.
It appears that in the 14th Century a man fashioned a silhouette of a snarling dog out of a sheet of leaded bronze and nailed it to the side of his house on the Headland in Hartlepool.
It has been discovered during excavations by Tees Archaeology before building work began on a sports hall.
Rachel Grahame, project officer for Tees Archaeology, said: "This is one of the most unusual archaeological objects to have come to light in the region.
"At some point in the past it must have fallen down a narrow gap between two buildings - perhaps during a storm - and been forgotten. Remarkably, it has survived the centuries."
The dog, which measures about nine inches across, has been examined and conserved at Durham University, but experts cannot agree on its purpose.
Stephen Sherlock, excavation director, said: "The teeth and eye are particularly crudely cut, suggesting that this is home-made rather than made by a craftsman. It might have been a Beware of the Dog notice or a sign outside a public house."
There is also speculation that the hound could originally have been a weather vane - copper tags and rivet holes around the neck suggest the head had broken off from its body and been mended at some time in the past.
Other holes on the edge suggest it might have been nailed to a board, perhaps as a sign. It has also created a further mystery, as parts of the skeletons of a dog and a cat were found alongside it.