said by TBBroadband:Only if it is not signed. Then again, it's a merchant agreement rule that Visa and Master Card both drafted and enforce. Sign the card with ID if not signed- no accept the card- card that is not signed is not valid until signed.
They are required to ask if the card is not signed. They can ask whenever they want even if the card is signed. You may want to re-read the merchant agreement from Visa. It is not against the rules to ask for the ID any more. It changed with the recent law changes with credit cards.