Why? Because getting people to obey the law could cost the city some speeding fine bucks! Maddening story out of Frisco, Texas (warning: locals hate it if you call their town "San Francisco"), reported by local TV station KHOU:

Ron Martin argues he has a First Amendment right to warn drivers of a police speed trap in his community after officers arrested him for violating the city's sign ordinance.

Officers handcuffed Martin along Eldorado Parkway near Preston Road last October for holding a sign that alerted drivers to a speed trap nearby.

"I observed a couple cars drive by traveling westbound waving at us," the police officer wrote in Martin's arrest report. "Mr. Martin was observed standing in the center median of the six-lane divided roadway … holding a sign in his right hand up over his shoulders that read 'Police Ahead.'"

When two officers left the enforcement area and drove over to Martin, he pulled out his mobile phone and used it to record his own arrest….

On Wednesday afternoon, he made his first court appearance on the misdemeanor charge.

"Ultimately, we're trying to do the exact same thing," Martin insisted. "I just don't wear a uniform. I'm the same thing as a speed limit sign, just reminding people that there is a limit here."…..

Still, Frisco police cited him for violating the city's sign ordinance, which says the person holding a sign has to be on private property.

Martin was in the median….The issue is bigger than a simple sign along a busy road, Martin insisted — it's free speech.