duxfan -
If you present your credit card with a "ask for ID" note written on the signature line, I hope you also always present your ID at the same time.
Speed is the name of the game, and signing your credit card (like you're supposed to, per the cardmember agreement) and having the merchant check the signatures is the fastest way to go. There's nothing more annoying than waiting for someone to dig up ID when asked to use a credit card or (worse) check. Maybe I'm a little impatient, but in NYC, speed is the name of the game.
Besides, I think a signature is more secure anyway. Unless you're a forgery artist, it's tough to make your signature look like someone else's. ID on the other hand is really easy to come by. Just look at the thousands of kids who buy alcohol or get into clubs every night with fake IDs.
d