You dont say exactly who the signature belongs to.
If it is of someone like Babe Ruth, Joe Dimaggio, or several other baseball players, it could be worth quite a bit.
Before you place a bid, you need to have it authenticated, and you need to get the provenance of the item.
WHERE and WHEN was it signed?
If you have access to the item, contact a reputable sports memoribilia shop and ask them if they can help you.
Ask them if they can provide someone that can authenticate the signature (WARNING, that could cost you a pretty penny).
If the seller refuses to allow you to do that, DONT buy the item because it is most likely a fake.