Depends on the state. Some states do emissions testing that fails such people, and officers are on the lookout for vehicles that are visibly violating the stand

Depends on the state. Some states do emissions testing that fails such people, and officers are on the lookout for vehicles that are visibly violating the standard. Other states are indifferent as long as you aren't assaulting others with it. Obviously, seeing as how they're doing it for attention, it's very unlikely that someone would roll coal with the intention of not blasting someone with soot.