I was signing the receipt for my credit card purchase when the clerk noticed
that 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
asked why, she explained that it was necessary to compare the signature on the
credit card with the signature I just signed on the receipt. So I signed the
credit card in front of her. She carefully compared that signature to the one I
signed on the receipt. As luck would have it, they matched.