Unsigned Credit Cards
It never ceases to amaze me that some people think that not signing their credits cards will protect them from thieves. It's fine if that's their way of making cashiers check their photo ID, but I've had many customers with unsigned credit cards get snippy with me for asking to see their ID. I had one woman icily tell me that she didn't sign it so that no one could steal her signature. But if she leaves it blank, any thief can sign their signature to the card and use it easily!