In my neighborhood, someone bought an old Crown Victoria (possibly a police interceptor) and did it all up like a cop car. On the side, the decal read (in large letters) NOT THE PO-PO. No blue lights. I think that makes the difference.
On the other hand, I haven’t seen that car lately.
Now, that you mention it, I have seen several Bluesmobiles out and about in the wilds of DuPage County, minus the optional HD PA system.
Bluesmobiles visiting Mount Prospect this weekend
https://archive.ph/dPi7S