17 U.S.C. § 1302: Designs not subject to protection

Protection under this chapter shall not be available for a design that is—(1) not original; (2) staple or commonplace, such as a standard geometric figure, a familiar symbol, an emblem, or a motif, or another shape, pattern, or configuration which has become standard, common, prevalent, or ordinary; (3) different from a design excluded by paragraph (2) only in insignificant details or in elements which are variants commonly used in the relevant trades; (4) dictated solely by a utilitarian function of the article that embodies it; or (5) embodied in a useful article that was made public by the designer or owner in the United States or a foreign country more than 2 years before the date of the application for registration under this chapter.