22 U.S. Code § 454 - Unlawful use of the American flag by vessel of foreign state
(a) It shall be unlawful for any vessel belonging to or operating under the jurisdiction of any foreign state to use the flag of the United States thereon, or to make use of any distinctive signs or markings, indicating that the same is an American vessel.
Source(Nov. 4, 1939, ch. 2, § 14,54 Stat. 11.)