Go go Gadget lightbar. I actually thought about that for my car only not a single rotator. It would have had to be a thin LED. Never got past wishful thinking. That and the large amount of space it would have taken where the cage is plus a lot of cutting up the roof.
I know most of you already know this, but keep in mind the Cadillac presidential limousines along with the vehicles the USSS travel in are airlifted in on a C-130 when the president flies into the country. The host country is then responsible for providing vehicles that provide additional support when the vehicle is traveling in the country it's in. Of course you're going to see Japanese vehicles mixed in with the American ones. Why "the Beast" is plated with a Japanese tag, however, I don't know.