Inappropriate!
Holding up funny signs during pregame shows is something of a college football tradition. Before Marshall-Rice today, a single sign in particular stood out. That would be the one that had "PENIS" written on it four times, using "ESPN" to help, acrostic-style.
Naturally, this exploded on Twitter. The sign appears to be a homage. Here's the same theme being used back in 2011:
So basically, "ESPN/PENIS" signs are like the Olympics: they show up every two years to unite the world with their magic.