Thankfully no signatures involved. You roll up, swipe/dip/tap your card in a reader on the gas pump, enter your postal code (archaic security measure from the pre-chip card era), wait a few moments for the electronic authorization (they pre-authorize an amount in the $75-150 range), then pump, and leave.

If you are paying cash, you generally have to go inside before pumping and prepay, and then go back inside afterwards to get your change, if applicable.