I saw a completely stealth police car the other day here in Colorado. It didn't have a light bar, or push bar in the front, but it did have "Sheriff" in flat black letters on the side of a gloss black car. I only saw the lettering because the light hit the car just right. Pretty sneaky if you ask me.
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong, it usually turns out to be impossible to get at or repair."
-Douglas Adams, Mostly Harmless