This came up recently, not sure which words to use to do a search however.
This is where the "Popular Tags" hack for vB sure comes in handy.
The thing about about Government approved highway paint is they make the suppliers for this type of paint make the paint to really be tough, they don't want it wearing off pavement that's driven over and over and over in all weather conditions by zillions of tires over the course of time and that makes removing it from anything really difficult.
As often as this problem is posted to all the detailing and niche forums you would think someone would hold the Government accountable and make them offer a solution to this type of problem.
Did you try a compound by hand with terry cloth? You can exert more power with your 4 fingers to a small area than any machine with a buffing pad. It's not fun but it's true.
Mineral Spirits
Turpentine
Lacquer Thinner
Would all be safe to try, I wouldn't recommend MEK or Acetone as both of these are pretty nasty to your skin and could dissolve your car's paint or at least soften and dull it.
Might give this a try too....
Motsenbocker's LIFT OFF 4
MOTSENBOCKER'S LIFT OFF 4
It's states it's primarily for Rattle Can Spray Paint. It was less than $8.00 so it wouldn't be to expensive to test out. Next to it were some other products for the same purpose but the Lowe's salesperson said they've tried them all for use in the Lowe's store and the Motsenbockers worked the best.
Here's what the website states about the product,
#4 Graffiti Remover
Mötsenböcker’s Lift Off® #4 Spray Paint Graffiti Remover is the only water–based, biodegradable and Green Cross Certified, by Scientific Certification Systems, graffiti remover in the world! It effectively removes all types of oil based paints, varnishes, lacquers and spray paints from all types of surfaces including: stucco, concrete, cars & trucks, brick, metal, plastic and more!
Features and Benefits
Spray Paint Graffiti Remover
Green Cross Certified
Low–VOC
Water–Based
Biodegradable
Safe for the Environment & User
Works On:
Oil–Based Paints • Varnishes • Lacquers • Spray Paints • Old & Fresh Paint • Acrylics • Primers • Enamels • Sealers • Aerosol Paint • Acrylic Enamels • Semi–Gloss • High–Gloss & More!
Safe On:
Hard, Soft, Porous Surfaces including: Stucco • Concrete • Cars & Trucks • Brick • Metal • Plastic • Street Signs • Utility Boxes • Tile • Vinyl • Plexiglas® • Aluminum • Stainless Steel • Fiberglass • Split Rock • Formica® • Slumpstone & More!