Is there a law stating you can’t have a protest sign with a picture on it on “skrool” property?
Affirmative Action IN ACTION!
Even there is, and it's applied to non student/staff during non school events, it's unconstitutional. It's public property, which is being used for a political function. Political speech used to be what the first amendment was understood to be about. Now it's about pornography, and covering up a veterans' memorial cross that happens to be on "public land", (in that case in the middle of the Mojave desert)
The cross is current boxed up, by order of the 9th Ciruit Court. A link to a high res photo of it is here
