Sure looks like a dealership (Exeter, Pennsylvania) ID or perhaps a city tag. The ornament does look like a auto ornament. Sure wish you took a picture of it laying on a table so we could see the top. It resembles some Cheverolet ornaments from years ago.
Very timely post, the Feds just arrested a bunch of the bigwigs in Exeter,Pa. Maybe you could sell the sign and post their bail for them,HaHa.....Joe McDonough
These were made of pot metal. A thin layer of copper then a thin layer of chrome. They corroded from the inside out. Like a zinc penny on the beach. Tony