First, some states do have laws against writing down any info from an ID or phone number in a credit card transaction, e.g., california, and I have sued under this law in California and obtained a settlement, including some cash to me as the class action representative.
Second, MasterCard's merchant report form can be used against any merchant who displays a MC logog and demands ID to use a signed card, or sets a minimum, or has a fee, to use the MC:
http://www.mastercard.com/us/personal/en/contactus/merchantviolations.html
I have spoken to VISA and they have the same rule, though you must report violations thru your card issuing bank - kinda weird as until you reach the upper echelons of the bank, nobody knows what your talking about. See
http://www.msnbc.msn.com/id/13806200/ns/business-consumer_news/:
SNIP
"Can merchants ask for ID when you make a credit/debit card purchase?
—Lorna M., New York, N.Y.
Visa and MasterCard have similar rules on this. In most cases and in most places, a merchant cannot ask for identification to process your transaction. If the clerk believes the signature on the sales slip does not match the signature on the back of the card, they can call the card verification center and may be instructed to ask for identification.
Merchants are required to ask for picture ID if the signature line is blank. You will be asked to sign the card on the spot. Visa and MasterCard rules say if you refuse to sign, that card cannot be accepted.
Instead of signing their card, a lot of people write “See ID,” or “Ask for ID” in the signature line. They think this will reduce their risk for fraud. The fact is this is not a valid substitute for a signature. If the card is not signed, it cannot be used."
And i have heard AMEX, which used to be silent on the matter, now prohibits merchants, again, thru merchant agreements, to demand ID to use their signature cards - which is what credit cards are. in fact, under Mc and VIOSA rules, you can take a credit card in your name, give it to a friend, she signs it, and now she can use it and merchants must accept it, subject to a reasonable likness test between sig on slip and back of card!
So here's the deal - sign your card! And if you want privacy, issue yourself an authorized user card in a pseudonym - Like S. Clause. Or maybe just your first initial and last name. And sign it and use it. And if ID is demanded, refuse, explain procedures, if management does not allow, leave your stuff there, report them thru MC webiste merchant violation report form, and then follow up with corporate and local management - eventaully, they will get a letter from MC and yes in almost all cases, they will back down as MC may threaten them with fines.