Any HC who wasn't aware of taping signals by that time was a moron.
Signals to run plays they hadn't run during a game couldn't be stolen during a game. This was about spying on a closed team practice, not walking on the sideline with a camera; a video camera with a good zoom lens would accomplish the same thing from any number of places in the stands or up in the boxes.
With the spying they beat the Rams and their 7000 yard offense with Mike Martz calling plays. Without the spying, they lost to the Jets with 2nd-year pro Mark Sanchez at QB and Brian Schottenheimer calling plays. Probably nothing, though.