Never write "show ID" on a credit card...

[spdrun]

instead of signing. If you have a card physically stolen, you can call and cancel it. Or punch the person trying to steal your wallet in the nose.

But most fraud happens online. Online shops use address and/or ZIP code to verify the card instead of a signature. If you show a DL and your credit card, you've just given a sales clerk all the info needed to use your credit card online, or sell the info to someone who will. There's a good reason why cardholder agreements generally prohibit asking for ID.