We have a guest registration form that has place for THEM to write their card details, and then they sign it. Most ask why when i have already paid, and i say its our security, as we dont take a bond. We explain to them that "we can charge the card if you smoke, cook or damage the room, as you have written your number on there and you have signed it giving us permission to do so". Once they have left we shred the form. Some dont like it and wont fill it in but mostly they do. A motel in Sydney, actually photocopied their notice and I show it to those customers that say, they have never heard of it before, and have never had to pay a bond or give pre autho.
Realistcally, its like locks on doors...it only keeps the honest crook honest!!!
Our system also highlights if a card is dodgy, but we always take the first night's tariff to secure the booking (and the balance is payable on arrival)so that way we know when they book whether their card is ok.