To get that temporary auto importation sticker, you must own the car (not a commercial vehicle) or have permission from the lienholder to remove it from the USA. You will also need a major credit card in the exact same name as the owner/driver of the vehicle. When you leave Mexico, it is vitally important that you stop and have Mexican Customs (Aduana) remove the sticker from the car and give you a receipt, which you will want to keep forever; just in case you ever want to return with a vehicle.