You may also be interested in:
* SEIU v. City of Los Angeles - 114 F.Supp. 2d 966 (C.D. Cal. 2000)
* Boos v. Barry
* Edwards v. South Carolina - 372 U.S. 229 (1963)
* Gregory v. Chicago (1969)
* Bay Area Peace Navy v. U.S. - 9th Circuit (1990)
* Collins v. Jordan - 9th Circuit (1990)
Among others.
I'm sure they're just like Burk, which says that content specific is allowable if done correctly.