Nice and sleek, until the air get trapped in that area behind the cab !
This one doesn't count - it's not street legal :
I've been unsuccessful at finding a picture of a city maintenance truck with their signage up, but I know we have all seen them.
It's a giant flat sign on the bed of the truck that rotates. It has a flashing arrow to alert motorist of construction ahead.
Unfortunately, I see plenty of these trucks driving along with the sign still up, versus folded down.