You know it just mightshortysboy09 wrote: Wouldn't honking the horn and drawing attention maybe get the pistol turned in your direction? I like the reply as far as being a good witness, calling 911, and getting plate number and description. But, I wouldn't draw attention to myself and get the gun pointed in my direction. At that point I would feel my life is threatened and be forced to react.

Of course at that point you go from good witness with no justification to act, to good witness whose life is now being threatened with deadly force and the ability, legally anyway to act.
IANAL
I've been shot at enough to remember I don’t care for it. Unless it's job related, I'll keep out of the way if at all possible.. but.. Standing by in the shadows with a note pad while watching a lady being robbed at gun point is not likely to happen.