When I was a kid, and we were camping in South-Limburg by the Belgian and German borders, whenever us kids got bored during our walks through the hills and forests we'd count where cars would come from (yes, you can blame that for my current obsession with statistics).
Seriously, I think all the kids have (had?) this thing, like - oh! That car is from France! Cool! Or if there's a car with an unknown abbreviation on the sticker: where could they come from?
Oh yeah--there's forty-eight states in the contiguous United States, so we used to play a game on long trips of identifying "foreign" license plates (i.e., from another state), with the "winner" being he or she who had seen and confirmed the most plates from another state (only works if you're driving for a long time in one state--but outside New England, it is very common that one drives for hours in one state).
Additionally, this game was entertaining to small kids from one year to the next, because states used to issue new license plates each year, rather than stickers which went on the plates, and the color patterns of the plates would change.