17 USC 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

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(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.