Is Flashing (Your Headlights) A Protected First Amendment Right???

As long as I can remember there's always been the battle between Police, the State Patrol, and law enforcement vs. Drivers over the issue of flashing their headlights to warn other drivers about a possible speed trap.  I'm sure you've seen someone flash their lights at you and then not too far down the road--there is the cop car, ready to pull someone over for speeding.   People do this as a courtesy to other drivers to save them money.  BUT---IS IS LEGAL???

The cops say it is an obstruction of justice. The drivers say it’s a simple form of expression protected by the First Amendment in the constitution.  And, drivers are smiling because various courts in the states of Florida, Utah, and Tennessee have all looked at cases and found that flashing your headlights is protected speech. No word yet if we are free to flash those headlights here in North Dakota!  (Yahoo News)