Sheehan Arrested for Anti-War Sign Just Before SOTU

Annoying anti-war activist and buddy of Hugo Chavez, Cindy Sheehan was removed from the House Chamber by Capitol police because she had an anti-war sign, according to CNN's crawl. She was the invited guest of a member of Congress. I dislike Sheehan, but is there a law against sitting quietly with a protest sign in the Capitol? Hey, it might be indecorous, but what about the right of citizens to petition their government?