36 U.S.C. § 301 : US Code - Section 301: National anthem

      (a) Designation. - The composition consisting of the words and
    music known as the Star-Spangled Banner is the national anthem.
      (b) Conduct During Playing. - During a rendition of the national
    anthem - 
        (1) when the flag is displayed - 
          (A) individuals in uniform should give the military salute at
        the first note of the anthem and maintain that position until
        the last note;
          (B) members of the Armed Forces and veterans who are present
        but not in uniform may render the military salute in the manner
        provided for individuals in uniform; and
          (C) all other persons present should face the flag and stand
        at attention with their right hand over the heart, and men not
        in uniform, if applicable, should remove their headdress with
        their right hand and hold it at the left shoulder, the hand
        being over the heart; and

        (2) when the flag is not displayed, all present should face
      toward the music and act in the same manner they would if the
      flag were displayed.