It's just a matter of being considerate, if not a safer driver. God knows being considerate has become unfashionable these days!
A few weeks ago I was waiting to make a left onto a busy road. One car coming from my left turned into the road I was pulling out of. No, he didn't have his damn signal on. I could have pulled out, had I known he was turning! :| As he made the turn, I flipped him off. His car started slowing, so I figure that pissed him off. Or maybe he was going to back up and apologize... inconsiderate mofo!:disgust: