Missouri: Judge rules flashing headlights as speed trap warning is "free speech"

According to USA Today, a federal judge has ruled that flashing your headlights to warn drivers about a possible speed trap is protected as free speech under the First Amendment:

U.S. District Judge Henry E. Autrey in St. Louis on Monday issued a preliminary injunction prohibiting the St. Louis County town of Ellisville from citing and prosecuting drivers who flash their lights to warn of radar and speed traps. Ellisville's city attorney said there are no plans to appeal.

[snip]

Jonathan Turley, a criminal attorney and a professor at George Washington University Law School, said courts across the country are dealing with the same issue. In virtually every case except those still being decided, the person cited has prevailed, Turley said.

"This has sweeping implications for the First Amendment," Turley said. "What this citizen is doing is warning other citizens about the violation of law. People regularly warn others about the possibility of arrest. There's no difference between a verbal warning and a mechanical warning. Both are forms of speech."

Who hasn't done this while driving?

Who knew you could be cited with a possible $1,000 fine?