Only thing I hate worse than a mark, is a marked car

from Royce Da 5'9" (Ft. Travis Barker) – Legendary Lyrics on Rap Genius

Meaning

A marked car is a type of police car that initially appears to be just another car until you notice the subtle police markings (See the top of the car in the picture below.)

So, the only thing Nickel hates more than “a mark” (a term which could be used to describe a variety of things, but mostly means a weak ass person) is a low key police car.

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