I think Peyton explained it as something more or less akin to “HUT!”. The offense would know which occurrence (first, second, third, ...) was the hike signal. The idea was to use the first call on non-critical downs (e.g, 2nd and 6 on your forty in the first quarter) and save the trickery for situations where it could make a difference (e. g., third and four on the opponent’s 11 in the fourth quarter).
Ahh... so there was no use for it since they never got to a situation where it would make a difference :-) I did hear him, during the week leading up to the SB, having a little fun with the reporters about it. But that got play because it was the most recognized call, there were certainly others. And he did voice play changes alot amongst the linemen because they obviously can't watch for hand signals.
But in this case, getting away from Omaha (and other actual audible calls) in favor of hand signals, was this a case of perhaps overthinking and confusing his own players or allowing his team the opportunity to miss his hand-signaled "audibles"? The old school in me says you dance wit' who brung ya'. Just a thought...