Not trying to be crass so please don't take it that way, but to buy a sign on eBay
and wonder what it it worth is kind of an obvious answer. eBay
is the world's market place. If there is something rare it will be found by serious collectors, and it will be bid on/up accordingly. Condition is everything, and that rings true with the common or the rare. If you are happy with the $50 you paid for it, then enjoy it!