Is it legal?

YES and NO

          YES! Free political speech is a fundamental right under the First Amendment.   It is your right as a citizen to display non-commercial signs and banners, with some exceptions. Rules regarding signposting along roadways vary from state to state, and locality to locality.  So, call your local department of transportation to find out more. Ask for public relations and say you'd like to put up some American flags and "Support the Troops" signs... they will likely be more than helpful. Don't feel bad if that's not precisely what you intend to put up: this is America, and the rules apply equally to all points of view.

NO! Again, the rules vary from state to state, but here in California, your right to political self expression ends exactly 600 feet from the Interstate, and failure to comply may run afoul of the law notwithstanding that nothing in the Streets & Highways Code or Outdoor Advertising Act expressly bars political expression in those areas.  Although it remains unresolved whether they are constitutional, some local laws may be used to keep you from speaking out on the roadways.  The stated reason for limiting your right to political expression is that such signs present a safety hazard due to their being a "visual distraction" to drivers, which is perfectly reasonable just as soon as they move every damn billboard, commercial sign and jumbo-tron screen 600 feet from the freeway as well. So long as my local car dealer's allowed to show commercials on a thousand square foot TV right next to the 405, you can call my piece of cardboard a visual distraction, but I'm not buying it. Going by those rules, the only people allowed to address commuters are those who either rent or own billboards, which may be fine for the sake of capitalism, but it's bad for America.

Here at Freewayblogger, we feel that free speech is meaningless unless it extends to everybody: not just to those who can afford it. When the founders of this nation said that everyone was entitled to freely express their political opinions, they didn't mean we could hammer up a sign out in the woods somewhere, they meant we could hammer it up right in the middle of the town square. Why? Because that's where all the people were.

It is our contention that the town square of colonial times has now become the interstate: for better or for worse, that's where all the people are. With this in mind, we feel it is our God-given and constitutionally-granted right to post our messages on the interstates, freeways, or wherever-the-hell-else-we-think-people-will-read-them and we're willing to fight for this right all the way to the Supreme Court.

But you'll have to catch us first.