The flashing of a car's headlights is a near universal warning that a police officer lurks nearby, eager to issue an expensive speeding citation. After the town of Ellisville, Missouri threatened $1000 fines to discourage the practice, US District Court Judge Henry E. Autrey stepped in Monday to remind the town that it is perfectly legal.

On November 17, 2012, an Ellisville police officer ticketed Michael J. Elli for using his headlights to warn about a radar trap that had been laid on Kiefer Creek Road. Elli was charged under a municipal ordinance that prohibits "flashing signals" on anything other than school buses and emergency vehicles.

Elli was told his purported crime carried a $1000 fine and points against his license because the offense was considered a moving violation. The charges were dropped after Elli entered a not guilty plea and took steps to fight the accusation. The state chapter of the American Civil Liberties Union (ACLU) took up Elli's cause as a class action suit, alleging violations of the First and Fourth Amendments.

"Defendants caused plaintiff to be pulled over, detained, cited, and prosecuted in retaliation for plaintiff's communication of the message that approaching drivers should proceed with caution," ACLU attorney Anthony E. Rothert wrote.

The city now says that it will not enforce its ordinance, but Judge Autrey was not convinced by this promise.

"Even assuming, arguendo, that plaintiff or another driver is communicating a message that one should slow down because a speed trap is ahead and discovery or apprehension is impending, that conduct is not illegal," Judge Autry wrote in his preliminary order. "The chilling effect of Ellisville's policy and custom of having its police officers pull over, detain, and cite individuals who are perceived as having communicated to oncoming traffic by flashing their headlamps and then prosecuting and imposing fines upon those individuals remains, regardless of the limited special order."

The court granted a preliminary injunction on the grounds that Elli is likely to win on his First Amendment claim. The ongoing suit seeks a permanent injunction against prosecution of motorists in Ellisville for headlight flashing, but the plaintiffs want to see the precedent apply throughout the Show Me State.

"After filing suit, the ACLU was contacted by many other individuals complaining of similar policies by other municipalities," ACLU-Missouri Executive Director Jeffrey A. Mittman said in a statement. "It is important that law enforcement officers in other jurisdictions take note of this federal court decision and the ACLU-MO's commitment to free speech."

A copy of the decision is available in a 120k PDF file at the source link below.