Is this guy in the wrong? What's the harm?

Ron Martin, 33, from Texas was arrested after he was caught warning drivers that cops were ahead with a sign that he made. The sign, which is made professionally by Martin, said "Police Ahead".

Martin says that he was doing nothing but letting people know that they need to slow down. He explains that it's "almost like doing what a speed limit sign would."

Technically, though, he did break a law. A city ordinance states that anyone holding a sign must be on private property.