<prompt> Human: I recently took a good look at my debit card and it saysAuthorized Signature, Not Valid Unless SignedWhat is the purpose? Ive never had a merchant check nor deny me a purchase because it was empty. I also recently got my first credit card and it has the same empty space for me to sign.I looked up online and it pointed out that a thief could sign it for me and then it would match their signatures. Whats stopping a thief from imitating my signature?  <response>: Well looks like all my cards arent valid as none of them are signed 