The Washington Supreme Court struck down a county noise ordinance forbidding honking car horns for purposes other than public safety. The Court ruled that the ordiance was overbroad in limiting legitimate expression. The decision came in a case in which a woman was arrested for honking her horn in front of a house of a person who protested that she was raising chickens violating homeowner association rules.
A justice writing for the majority set out several instances of horn honking that should be protected, “…a driver of a carpool vehicle who toots a horn to let a coworker know it is time to go, a driver who enthusiastically responds to a sign that says ‘honk if you support our troops,’ wedding guests who celebrate nuptials by sounding their horns, and a motorist who honks a horn in support of an individual picketing on a street corner.” -db
From a commentary for the First Amendment Center, October 31, 2011, by David L. Hudson Jr.