When store clerks ask for your ZIP code at the end of a transaction, it's not always to validate your credit card or keep track of where customers are coming from. Several "direct marketing" software services require only your name—gleaned from your card—and ZIP to figure out your address, phone number, and purchasing history, reports Forbes. With that kind of info, they know exactly what kind of marketing to target personally to you—and exactly where to mail it.
And now stores are becoming pushier about getting you to hand over that ZIP info. One woman was locked out of a store and refused a refund when she wouldn't give hers. In California, Williams-Sonoma was sued after a woman gave hers for their marketing database, thinking it was needed for a credit card purchase. The state's Supreme Court ultimately banned stores from requiring the codes. But not all ZIP requests are worth pulling out your tin foil hat over. One museum that asked Forbes' Adam Tanner for his digits says it's purely about knowing where customers are coming from. "We strictly utilize the information we receive to better understand the demographics of the market of those specific ZIP codes," says a spokesperson from Las Vegas' Mob Museum. (Read more zip code stories.)