I spotted this poster on an outdoor public notice board. The "No!" is in reference to political contributions and how giving or receiving gifts and money is against the law. The little yellow guy is called Meisuikun. He's designed to look like a ballot box. Those two black lines on the top of his head are the slots for ballots. He's got wings, too. Maybe that means your vote is just going to fly away and not really count?
This site explains all about the character (Japanese only). Even if you can't read the text, scroll down to the bottom to see some localized versions of Meisuikun as well as some photos of him hanging out with sports teams. And if you find yourself wanting a Meisuikun of your own, here's papercraft instructions on how to make one. Just print, cut and paste! You'll notice that he even has a little lock on his back instead of a tail.