At a minimum if you attempt to make eye contact and the person is obviously not looking at you, you will know it and take caution.

And all this armchair cycling nonsense is ridiculous. I ride my bike 70-100 miles a week at a blistering 12-14 mph. So that means quite a few hours. I seem to be the only one who doesn't whine about the evil cagers. I must be doing something right.