Greg Schiano has completely lost the fan base. If recent polls showing 90% of people wanting him gone don't show this, then the fact that people are spending money to get him out of town probably does.
I've heard people say that there are billboards all over town, so the sentiment is fairly widespread. Then again, it appears to be sponsored by a radio station, so perhaps they're just doing to get some attention and listeners. That happens, too.
Whoever put up that billboard, one thing is clear: Bucs fans are fed up with Greg Schiano. Or at a minimum they are fed up with losing. If the Bucs can't beat the Panthers tonight, we'll probably see more and more public calls for Greg Schiano's firing. With a team that is 0-6 and faces new drama every other day, you can probably say those calls are justified.