Some people are cat people. Some prefer other animals. But no matter if you're a cat person, a dog person, an animal person or a person who doesn't like animals of any kind, it probably annoys you when cats jump on your car. You find the cat prints in the morning. You see scratches on your roof. The tarp has scratches in it so deep the paint is missing, despite your best efforts. There are plenty of ways to keep cats off your car.
Sprinkle cayenne pepper around the car. It has been known to keep cats away, and you don't even need to sprinkle it on the car, though that might be even more effective. After a few days, the cats should leave and not come back. If they return, try again or move on to another possible remedy.
Purchase mothballs and spread them out around your car, including on the car's roof. Alternatively, put the mothballs in a bag and hang them. The scent is strong, so beware. But cats don't like the scent either, and will stay away.
Set up an ultrasound pet alarm. An alarm, set off by a motion detector, scares off cats. It costs about $30 and is very easy to set up, even on the roof of a car.
Try a CatStop. This product works for up to about 20 feet by emitting a high-pitched sound that humans can't hear. It runs on batteries or electricity.
Use a ScatMat, which scares the animals off, teaching them not to go on your car. However, instead of an alarm, it uses static to alarm the cats. Depending on the size of the mat you buy, the ScatMat can cost anywhere from $20 to $420. After the cat learns to stay away, you can put it away until you need it again.