Don't blame your opponent because you have lousy encryption
I guess if it's in the rule book it's a violation; however, my reaction is pretty much what Old33 said at Volokh.com:
“What strikes me about all this is that the defensive signs, etc., are all in plain sight. Anyone on the opposite side of the stadium can watch the signs with binoculars.
If we were talking about stealing an actual playbook, or intercepting the headset communications of the opposing team, I can see how that's a problem.
But where is the expectation of privacy in defensive (or offensive) signs being relayed by hand signal with 75,000+ witnesses?