Cops ask people they pull over if they have any weapons or cash in the vehicle, and people are either intimidated or naive enough to answer truthfully. The last time I was pulled over, years ago, I had about $50 in my wallet and the cop asked me if I had any cash. He was visibly annoyed when I responded with "uh, your asking me if I have a wallet?" and gesticulated with the wallet I already had in my hands to show him my ID. He could already see that I had cash in my wallet, but that's not what he was asking about.