FREEWAYBLOGGER.com
A cool site from somone who posts signs on the freeway, and encourages others to do the same. Plenty of other examples there as well.
"When you handpaint a sign and post it in public it says two things:
1) whatever-the-hell you want it to say, and 2) that somebody cared enough about whatever-the-hell-they-wanted-to-say to actually paint a sign and put it where people could see it. If everybody who read this post put a sign on the freeway tomorrow, millions of Americans would see it. If everybody who read this post put ten signs on the freeway tomorrow, it could very well change the face of politics."
If you're inclined to do this yourself, try these:
I miss peace and prosperity.
In your guts you know he's nuts.
No surplus left behind.
Name one thing he's done right.
Who's gonna pay for this? Ask your kids.