Government regulation of speech on its own property is analysed by asking what kind of forum it is, and the answer largely determines the outcome.
Traditional public forums — streets, sidewalks, parks. Content-based restrictions face the most demanding scrutiny. Content-neutral time, place and manner restrictions are permitted if narrowly tailored to a significant government interest and leaving ample alternative channels.
Designated public forums, opened by the government for expressive use, are generally treated like traditional forums while they remain open.
Limited public forums, opened for particular subjects or speakers — a school board’s public comment period, a community room. Restrictions must be reasonable in light of the forum’s purpose and viewpoint-neutral.
Nonpublic forums, government property not opened for expression. The same reasonableness and viewpoint-neutrality standard applies, and it is the easiest for the government to satisfy.
The line that recurs in municipal practice is between subject-matter restrictions, which a limited forum may impose, and viewpoint discrimination, which it may not. A council may confine comment to agenda items; it may not permit supporters and exclude opponents. Rules about decorum are lawful in principle and become unlawful when applied to remove critics.
Prior restraints — permit schemes and licensing — require narrow, objective criteria that leave no unbridled discretion in the official deciding.