10 U.S.C. § 771 : US Code - Section 771: Unauthorized wearing prohibited

      Except as otherwise provided by law, no person except a member of
    the Army, Navy, Air Force, or Marine Corps, as the case may be, may
    wear - 
        (1) the uniform, or a distinctive part of the uniform, of the
      Army, Navy, Air Force, or Marine Corps; or
        (2) a uniform any part of which is similar to a distinctive
      part of the uniform of the Army, Navy, Air Force, or Marine
      Corps.