Help me with this one

As I was driving home this evening, I glanced up, as always, at the pedestrian bridge over Campus Drive. You don't need to pick up the paper in Madison to figure out what's playing in the theater or concert hall; all you need to do is look up at the bridge and you will see signs announcing anything from jazz artists, to musical hits, or the coming of any number of noteworthy performers.

But what I saw today was a guy holding up a huge sign that read: "NO MORE SOUR JUICE."

What am I missing here? It's one of those things that's lost in translation, right? Probably everyone else is driving home and thinking "yeah, no more of that stuff, right on!" Or, is it that the person with the sign was complaining that there is no more sour juice to be found anywhere, it's all sweet, damn it! Or what -- an irreverent rock band, aka Sour Juice, that should not be permitted entry into our concert halls or nightclubs? Truly, I'm in the dark.

If you know the significance of this, write me. My ignorance is killing me.