Would board members consider the USC win last year as a signature win?
USC was undefeated, coming off a win over #11 at the time Arizona, had the leading Heisman candidate, an offensive wizard as a coach, etc. And Marcus and co beat the shit out of them. It was so bad that "Mahomes-esque" all world QB who painted his fingernails for the event didn't even finish the game.
To me, if the term means anything, that was it.