It is not a US plate at all from the looks of it. They most likely brought the car with them. The car is luggage. All they have to do is flash their diplomat paper(s) and they move on. That is if they even stop if police try to pull them over.

Yep, US Diplomat/Consoul/etc plates look like this:

I guess she only likes Ricky Stenhouse Jr. tapping her from behind?

Car & Driver