You really think you're going to be able to spread any meaningful message on a 9 by 6 meter display, while people are going at 55 mph? It's like how people sometimes put those ads on the side of the road that are longer than a bus. "Do you want cheap, affordable jaguars? Well, then stop by Mickey's, take a left three miles down the road!" Honestly, between trying to avoid the other drivers who are attempting to kill you, reading the sign posts to know where the heck you are, and keeping your eyes on the road, I don't think a lot of people will find the time to read it. Now porn with the message to rise against the oppressors scrolling by at the bottom of the screen, THAT would've had a huge effect.