I just read a brief article on PoliceLink that was titled Interesting Origins of Police Words. The article gives you just a few terms that relate to Law Enforcement, like graffiti and cop, so I thought I would toss a couple more out there. First, I must agree with comments on the article; the origin of the word cop was supposedly coined in old New York. Officers on foot beat would wear overcoats with copper buttons and the nickname cop reportedly came from that reference.
We can't ignore the slang term, Five-O, when on this topic. You have to remember the TV show "Hawaii Five-O." The late sixties show ran for a long time and the term Five-O referred to the police unit. Today it simply refers to the police or a police officer.
Older, but not forgotten is The Man. The Man has always referred to a person in authority or control and was tossed over as slang for police officer as well.
It is not so much that we are looking at the origin of words, which goes beyond a simple history, but it is interesting to look at how the terms came about. There are plenty out there. If you have any, throw them in the comments and see if we all agree on the meaning.