I'm not sure if it's a direct violation. The rule refers to a message that is meant to "incite" violence. Brandenburg v. Ohio (1969) says speech that is meant to incite "imminent lawless action" is not protected speech. Because the rule could be read to refer to that standard, it is not a direct violation. However, it is not clear from the rule that it is that limited and so it could cause people not to express themselves where the First Amendment would apply. In other words, the rule can have a "chilling effect" on free speech and so it violates the First Amendment.
Well, the rule does say “incite” and “immediate,” but since without perpetrating violence against the language there is no way an ad that may or may not make someone angry, and that angry person may or may not perpetrate violence is guilty of inciting immenent violence there is no way it passes the Brandenburg test. Therefore, it is out and out violation of freespeech and not a chilling effect.
On the other hand, it may be like in school where the authorities have broad proprietary powers. That is to say you have the right of free speech but not the right to force the transit authority to put things on their wall at your whim. In which case it isn’t a free speech violation nor a chilling effect. But I don’t really see how it can be a chilling effect and not restriction of speech.