In the Des Moines Register today, Jeff Eckhoff wrote a story today about businessman Anthony Herman in Polk City, Iowa. Apparently, Mr. Herman is involved in several legal battles with the City of Polk City, and began using a sign on his property to display his distaste for the City using choice statements about the Mayor and members of the City Council. The Polk City city council "has no plans to try to interfere with his right to free speech."
Pursuant to a 1971 U.S. Supreme Court case (an oldie but a goodie), Polk City might face a tough challenge regulating Herman. In Cohen v. California, the Supreme Court ruled that "the State may not, consistently with the First and Fourteenth Amendments, make the simple public display of [an] expletive a criminal offense." Justice Harlan famously wrote that "one man's vulgarity is another's lyric."
As individuals, the Polk City Mayor and City Council could try to sue Herman on defamation grounds. However, the City officials would probably be considered "public officials." To prove libel (written defamation), the Polk City officials need to prove that 1) the statements were defamatory; 2) of and concerning the city officials; 3) the statements were published; 4) the statements damaged the reputation of the officials; 5) that Herman knew the statements were false; and 6) that his statements were made with reckless disregard of the truth.