As you might guess, a permanent marker stain can be difficult to remove. But with the right cleaning materials you can remove marker stains from your car.
Removing a stain from a car's interior works best if you can treat it sooner rather than later. Test an inconspicuous spot on the interior by using a cotton ball with a small amount of acetone in an area on the interior. If the acetone doesn't cause bleaching to the upholstery, you can gently rub the marker stain with a cloth and acetone until the spot disappears. You can rinse the cloth out with cold water to remove the remaining ink.
Removing a permanent marker stain from your exterior can cost several hundred dollars if done at a body shop or dealership. There are, unfortunately, no products that are made just for this purpose either. Many people have had success removing permanent marker stains with simple aerosol hairspray. To do this, simply spray the offending area with the hairspray and use soft tissue to remove it. The alcohol in the hairspray will generally break down the marker stain without damaging your car's finish. Just be sure to wash all of the hairspray off your vehicle when you're done.