A Black Audi has symbolism in China, it means mid grade official at least (Audi beijg in China much longer than anyone else). Normal police don’t have access to that of course, if you see police in a black Audi wearing suits and sunglasses, they are very elite and are often involved in political crimes (Eg Party enforcement).

As an example, normal police in Beijing walk on egg shells since many people have lots of connections to bare. So a bunch of rich kids smoking weed isn’t something they will go near, so those are busted by the Black Audi people (who have strong enough connections to resist whatever).