What statutes govern the directing of traffic by citizens in Massachusetts?
Yesterday afternoon during Friday rush hour, I came upon a 2 car head on collision at a blind curve in my area. I am a hospital employee and have training in emergency response so I stopped to help when I saw a young man clutching his eye. 

I put on my poncho and did my best to make clear signals to drivers. All the participants were physically fine, but there was a heavy rain and if I hadn't acted, I suspect there would have been a 2 hour line of traffic at best or a series of further collisions at worst. There were no problems, and I left when the police arrived. 

As I was leaving, a police officer thanked me but cautioned me that it was a legal liability. My thought on the matter is that if an accident had occurred, it would be because drivers ignored my signaling. So who knows who would be in trouble?