Hey there, I'm really late to the party, but I live in St Louis and it's not uncommon to see that sign. The protesters don't actually believe what it says, they're really protesting the idea that people think it's okay to defend the robber. There was a situation where a man was holding up a gas station and threatened the clerk. Another man stepped in and told him to drop the gun, and when turned and confronted, shot the robber. The parents sued saying their son (who robbed the store) did nothing wrong. These signs sprung up exponentially after that.