As far as I understand, they were not doing anything like what Michigan was doing.

To be clear: Sign stealing is legal to a certain extent. There is no "unwritten rule" or honor system here. If your offensive play calling was so easy to decode that an opponent could look at your play calls and figure them out, that was perfectly legal. UU looking across the field and seeing that an opponent was holding up a sign with a duck and a sign with a Mazda and then inferring that this meant that the next play was a pass is completely legal.

I do feel that it is likely that the helmet comms now make this tactic obsolete and it may be removing an advantage that some teams were using. But it was not illegal.