Likely for the same reasons that private security companies also make their cars look similar to police cars.Not to start a debate, but from a good distance I believe the small "police" on some of the cars could easily go unnoticed.
And obviously the MCP cars are deliberately painted to resemble NYC patrol cars as much as possible. So one just has ask to himself, "Why?" I think the answer is obvious.
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How often do you think that private security companies get in trouble for "impersonating police officers?"