Sprayed on. looks like just off the self spray paint.
Lacquer thinner will typically remove spray paint pretty easily, but you do have to watch out for what is under the paint, especially if there is any plastic. The Acetone in the thinner (one of the various solvents in it) will dissolve plastics such as ABS.
What about brake fluid? Dot 3? Any suggestion for removing off the plastic as well?
Why not use a pressure washer? I've never tried it, but that's always been my plan if I wanted to strip a painted AR. Am I missing something obvious?
Brake cleaner will usually take off rattle can.