Is it free speech to Flash your high beams?

OK, imagine this, it can be daylight, it can be nighttime. You're driving down the road, somebody is coming toward you, and they start blinking their high beams. They're trying to get your attention to warn you about something, but what could it be?

If you're on 97 A, they're probably warning you of either a deer on the road or some of those Big Horn sheep just hanging out on the side of the road watching you go by. 

There's also another thing that happens when people are flashing their high beams at you. They're warning you that the State Patrol is waiting for you with their radar gun to bust you 

But here is the question. 

Is it legal to flash your brights at an oncoming driver to warn them that there's a speed trap up ahead? Could this technically be construed as obstruction of justice? 

I had no idea this was a thing, but apparently it was illegal in some States and counties all across the US. 

According to ktla.com, this was true across the US until 2014 and then it changed.
“A federal court in St. Louis ruled that drivers are allowed to flash their lights to warn other motorists of nearby police and speed traps. The court ruled that it’s a first amendment right.”

FooTToo

You got it, it is your “First Amendment Right” to flash your brights, to warn somebody that there's a speed trap ahead. It makes me wonder if there's any other kinds of signals I can use while I'm driving that would extend my free speech rights to, I don't know. Signal somebody that they're an idiot and need to get off the road right away.  

Maybe there's a special signal to indicate that people need to lookout, because I've got to find an emergency stop at a Mini Mart and then hit the bathroom.  

What would the signal be to inform an oncoming driver that their car is criminally filthy and needs to be washed? 

Drive safely, be careful and if you have to flash your lights. You better mean it. 

 Is Flashing Brights to Warn of a Cop Ahead Against the Law? (popcrush.com) 

Headlight flashing: What it really means and is it illegal? | KTLA