It takes a real genius to steal a vanity plate such as that and actually try to put it on a vehicle. Just a hunch but it was probably stolen from the vicinity of the second "person of interest" (younger guy) but I doubt that it's connected. Some treehugger teenager probably wanted to put it on their bedroom wall.
That's an interesting theory.
I thought maybe Fawley tipped them to it since he is a license plate collector or possibly he remembered it from the night he was supposedly kidnapped or maybe the Ohio plates were put on her car and her plates were put on the GRN ERTH plated car, which would leave the GRN ERTH plates missing.
BTW, the skateboarder guy's name is Jesse Schulz. Now, we have a name.