Vote for the wolf ... to send them a message
It's clear that this was originally a Greek cartoon, since the Greek writing at the bottom of the campaign poster identifies the wolf with the swastika armband as a candidate for the Greek neo-fascist Golden Dawn party. Then someone translated the caption into French, possibly adapting it in the process.
For readers whose French is even weaker than mine ... what the sheep in the cartoon is saying can be roughly (though not literally) translated into English as: "I think I'll vote for the wolf. That will send the shepherd a message!" (borrowing a formulation from George Wallace). Protest voting, in other words.