Even the Columbus Dispatch & Eleven Warriors reported this to be true.
Secondly, I think it's a really bad argument when people claim it takes from Spring to be able to change and learn signs when almost everyone in the country now has been saying that in-game sign stealing is very common and teams have worked to combat that for a long time. If it's that common in-game, teams have been used to changing up signs and systems consistently. I simply don't buy the argument it takes so long to change it up. Again, I could be very wrong, but it sounds like another angle for some to paint Michigan in a corner of being a cheater.
Lastly, Stroud.. Stroud had a MONSTER game. I don't get the angle about best NFL rookie and trying to act like Stroud had such a bad game against UM because UM had the signs. Stroud played lights out. He had 349 yards passing against Michigan and 348 against Georgia. Claiming Michigan shut him down isn't really an accurate statement.
Good.. we can go back to disagreeing 
On changing signs, this is my guess:
If I were designing a system, I think I'd teach my team say three complete sign systems. So let's say the sign for a TB run off LT is:
- A picture of Jim Tressel
- A picture of John Cooper
- A picture of Earle Bruce
Then, as per usual, I'd have three or four signalers and only one of them would be "hot" with the other two throwing up dummy signs.
Thus, I would have two ways to confuse opposing sign stealers:
- I could switch between system 1, system 2, and system 3, and
- I could switch the "hot" signaler.
If I had four signalers, this would effectively give me 12 systems:
- Signaler 1, system 1
- Sig 1, sys 2
- 1,3
- 2,1
- 2,2
- 2,3
- 3,1
- 3,2
- 3,3
- 4,1
- 4,2
- 4,3
If the opposing team was using the legal (Rain Man) method to decipher my signs, I *THINK* this would be enough to stay ahead of them for a game.
The whole game changes if the opponent already learned all three of my systems from advance in-person scouting with video and time to rewatch and code-break by reverse engineering my signs.
At that point they would enter the game already knowing that my three alternative signs for TB run off LT are the three aforementioned pictures of past tOSU coaches. Once I run that play, they'll be able to figure out which system I'm using and who the "hot" signaler is.
