17 U.S. Code § 1302 - Designs not subject to protection
Designs not subject to protectionProtection under this chapter shall not be available for a design that is—
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;
different from a design excluded by paragraph (2) only in insignificant details or in elements which are variants commonly used in the relevant trades;
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.