I’d secure it myself, then bring it into the nearest police station. First, however, I’d photograph the hell out of where I found it, and even try to find a witness or two who’d swear up and down that my story was right.
And don’t touch it, pick it up with a cloth or paper towel so your fingerprints don’t get on it, or mess up prints that might already be there. That might be evidence that could put a scumbag in jail.
Take the gun, load it with blanks and use it to shoot back at the next helicopter fake-strafing the freeway.
That should collapse the Media wave-function.