Free Speech or Inciting Violence?

Does this billboard and associated stickers illegally incite violence, or is it just legally sharing an opinion? Should it be removed or remain? What if anything should happen to those that created it? *

*For those that are unfamiliar with U.S. law, most hate speech is protected, but it becomes illegal at a point where imminent violence is being incited. The Supreme Court has held that government cannot punish inflammatory speech unless that speech is "directed to inciting or producing imminent lawless action and is likely to incite or produce such action." Inciting violence is a third degree felony.