When cashiers ask for personal information, it's okay to decline. By Susannah Snider, Staff Writer May 1, 2011 California shoppers who pay with plastic will be a little less forthcoming with cashiers, thanks to a state Supreme Court ruling prohibiting merchants from asking cardholders for their zip codes. Coupled with your name, those five digits help retailers pinpoint your address, track your spending, pack your mailbox with customized junk mail or sell your personal information.Other states may follow with similar rulings, and some retailers might stop asking for zips to avoid lawsuits. But here's the kicker: Many shoppers don't realize that they've never had to provide their zip code when asked. You're required to produce it as a fraud-prevention measure -- for example, at the gas pump or online, where a cashier can't compare your signature to the one on your card. You can also refuse to show your driver's license when using your card in a store; MasterCard and Visa say a signature is enough, and that merchants who refuse a transaction aren't following the card companies' rules. Folks who don't sign their cards (also against the rules) should expect to show corroborating ID. Moral of the story: Don't automatically volunteer personal info if you'd rather not. Chances are, it's not required.