“The Constitution says that Congress (and the States) may not abridge the right to free speech. This provision means what it says. We properly read it to permit reasonable regulation of speech-connected activities in carefully restricted circumstances. But we do not confine the permissible exercise of First Amendment rights to a telephone booth or the four corners of a pamphlet, or to supervised and ordained discussion in a school classroom.”
Tinker v. Des Moines Independent Community School District, 393 U.S. 503 (1969).