The auto motion plays in singleback formations are mostly counters and powers and while the motion can give away the snap count giving you the chance to blow up the play, some people have trouble with getting faked out on the play action and get beat deep. I mean you see the motion and know its auto motion, so you time the snap and ... oops.. lol
anyways since the auto motion playaction plays are based off of counters and powers, the easiest way to tell is to watch the guard. If he pulls, its a run, if he blocks down, its a pass. On the pa powers and counter the guard doesnt pull. There are some zone runs with auto motion that have play action off of them so watch out. Just learn to reconize power and counter out of those formations.
Come to think of it someone has to have put this out there at some point but I just discovered it on my own and wanted to share.