‘Overpasses’ Anti-Obama Protestors Arrested in Missouri

The President Obama bus tour in Upstate New York is bringing the topic of 'Freeway Blogging' to the forefront.

Freeway Blogging is the act of posting banners on overpasses to expose your message, either for promotion or a political agenda, to drivers on busy highways.  

The video featured in this story shows a protestor being arrested after refusing to terminate his demonstration on an overpass, crossing a busy highway in Missouri.  The protest was part of an 'Impeach Obama' effort inspired by Overpasses,org.  Similar banners have been hung on overpasses in Upstate New York, including one spotted on the New York State Thruway, near Syracuse.

So, is it legal?  Is this an act that is covered under free speech rights guaranteed by the U.S. Constitution?  Should the protestors have been arrested?