In the spirit of Jan's funny bumper sticker thread, I saw a license plate today at a dental clinic:
IFLOSU
My all-time favorite plate was on a white VW Rabbit: "HARVEY"
I also liked "OWLBCNU"
And once, in my younger and considerably more naive days (like, shortly after I got my license), I followed a car for blocks until I figured out what "HEYMOFO" meant

(apparently the state worker who approved it didn't get it either!)
I always wanted one that says "POETIC," but nobody ever gets it and it ruins the fun if you have to explain.