If this has been on long and in the sun, it may not come off as it has probably etched into the surface.
If you can clean it off: Rubbing alcohol, Simple Green, or ammonia with soft cloth.
If it is etched in: Try a Mr. Clean Magic Eraser. Try a clay bar. Try a light rubbing compound followed by polishing compound using a buffer. Test these somewhere first.
If this all fails - wet sand with 2000 and recoat.