http://www.law.cornell.edu/wex/index.php/First_amendment
First Amendment Rights have been brought up recently by the arrest and removal of 2 women at the SOTU address. The above link is where I found an overview of the First Amendment to explain my view of why I thought they were wrong in using the writing on the shirts as a reason to be removed.
The most basic component of freedom of expression is the right of freedom of speech. The right to freedom of speech allows individuals to express themselves without interference or constraint by the government. The Supreme Court requires the government to provide substantial justification for the interference with the right of free speech where it attempts to regulate the content of the speech. A less stringent test is applied for content-neutral legislation. The Supreme Court has also recognized that the government may prohibit some speech that may cause a breach of the peace or cause violence. The right to free speech includes other mediums of expression that communicates a message.
The case of Cohen v. California - 1971, was similar to this in that it dealt with the writing on a jacket in public.
http://www.bc.edu/bc_org/avp/cas/comm/free_speech/cohen.html
The ruling :
It is, in sum, our judgment that, absent a more particularized and compelling reason for its actions, the State may not, consistently with the First and Fourteenth Amendments, make the simple public display here involved of this single four-letter expletive a criminal offense. Because that is the only arguably sustainable rationale for the conviction here at issue, the judgment below must be
Reversed.
I'd say that Cindy Sheehan has a good case.