You can go through a pretty long judicial career and never face litigation regarding protestors’ rights and police conduct.  But, if confronted with this type of litigation, good judges scramble to find the best authorities.

It is in that spirit that you might want to read this piece:

Fair Warning

Caleb M. Hayes-Deats

 United States Department of Justice – Southern District of New York

November 3, 2013

Abstract: 

Protesting has become an integral part of American politics, so much so that federal Courts of Appeals have recently restricted police officers’ power to arrest demonstrators who have concededly violated otherwise valid statutes and regulations. Specifically, courts have found that, where demonstrators may reasonably, yet mistakenly believe that police officers have permitted their conduct, officers must give “fair warning” before arresting or dispersing those demonstrators. In § 1983 suits, courts have even found that demonstrators’ right to fair warning is “clearly established.” While the right to fair warning may be clearly established, its doctrinal roots are not. Ordinarily, the requirement of fair warning, grounded in the Due Process Clause, guides courts in their application of statutes. The cases mentioned above, however, consider not the content of statutes — indeed, the statutes’ applicability is frequently conceded — but instead the conduct of police officers and demonstrators. As a result, the courts that have recognized demonstrators’ rights to fair warning have not clearly specified whether the First Amendment, the Fourth Amendment, or the Due Process Clause creates that right. Identifying the source of this right is more than an academic exercise. Such identification will help courts expound the right’s contours and determine its future application. Ultimately, this Article argues that courts have unconsciously employed the right to fair warning as a less sweeping form of First Amendment review, one that applies First Amendment principles to officers’ enforcement of a statute, rather than to the statute itself. Only by attributing the right to fair warning to the First Amendment can courts both explain existing doctrine and vindicate the principles that earlier decisions have recognized when invoking that right.