I was signing the receipt for my credit card purchase when the clerk noticed I had never signed my name on the back of the credit card. She informed me that she could not complete the transaction unless the card was signed. When I asked why, she explained that it was necessary to compare the signature I had just signed on the receipt. So I signed the credit card in front of her. She carefully compared the signature to the one I had just signed on the receipt. As luck would have it, they matched.