Taping other teams is common. The Pats kicked a Jets employee out of an un approved taping area before the whole spygate thing.
http://sports.espn.go.com/nfl/news/story?id=3151217
What got them in trouble was ignoring the info sent out by the league about where the allowed places were.
https://en.wikipedia.org/wiki/2007_N...ng_controversy
"After footage from the actual tape was aired on Fox NFL Sunday on September 16, former Dallas Cowboys head coach Jimmy Johnson claimed, "This is exactly how I was told to do it 18 years ago by a Kansas City Chiefs scout. I tried it, but I didn't think it helped us." Johnson also said, "Bill Belichick was wrong because he videotaped signals after a memo was sent out to all of the teams saying not to do it. But what irritates me is hearing some reactions from players and coaches. These players don't know what their coaches are doing. And some of the coaches have selective amnesia because I know for a fact there were various teams doing this. That's why the memo was sent to everybody. That doesn't make [Belichick] right, but a lot of teams are doing this."[23]"
I'd have to say that any team that doesn't change their signals somewhat regularly is pretty foolish. Especially if they use the same signals for over a year.
Oddly, Baseball teams formally exchange annotated video of every at bat.
One of the books I have talks about Varitek altering pitch signals based on a formula involving info from the scoreboard, so the signals varied according to the inning and situation. The complexity was to avoid someone stealing signals.
Steve B