three plastic animals rule
n.— «In 1995, after ACLU sued, Jersey City added a six-foot-high Santa Claus, a three-and-a half-foot-tall Frosty the Snowman, a four-foot-high sleigh, Kwanzaa symbols and a sign explaining that it was celebrating the diverse heritage of the people of Jersey City. This has now come to be called the three plastic animals rule.» —“Eisgruber leads discussion on religious freedom” by Viola Huang in Princeton University Daily Princetonian (Princeton, N.J.) Dec. 14, 2005. (source: Double-Tongued Dictionary)