I agree that probably some degree of this goes on everywhere; it'd be difficult or impossible to ignore signals sometimes. I think the AU sideline probably makes less or no attempt to hide that they're doing it. This is consistent with the overall attitude of the program, if you believe that the hire of Chizik was an organized plan to improve recruiting by paying players, knowing full well the NCAA was weak and could be fought by good lawyers if caught.
I've never been a FB coach or tried to organize sports signals, but I assume if you know you're being read you can actually hurt your opponent with fake or changing signals. I don't know why they don't just hold up a big number and change everyone's armband every series.