> Written by Virginia L. Vile, published on January 1, 2009 last updated on July 5, 2024 It's an older article and might need further updating. You can also check whether it is coded as illegal in your state. > The practice, common among motorists, of flashing headlights to alert other drivers to an upcoming patrol car has been claimed as a form of expression protected under the free speech clause of the First Amendment. Thus far, courts have generally interpreted the practice as protected free speech.