Northwestern is one of many college football teams to use big boards to signal in plays. It helps speed up tempo, and confuses opponents who might be trying to recognize play calls.
Northwestern's boards against Duke featured an interesting cast of characters:
Yes, that's ESPN Radio host and noted Northwestern alum Mike Greenberg in the upper left. In the upper right is Teddy Greenstein, who used to cover Northwestern football for the Chicago Tribune, and still covers Big Ten football for the Tribune.
And in the bottom right is a Chicago Blackhawks logo.