Sec. 9. Conduct during hoisting, lowering or passing of flag

United States Code
TITLE 4 -- FLAG AND SEAL, SEAT OF GOVERNMENT, AND THE STATES
CHAPTER 1 -- THE FLAG

During the ceremony of hoisting or lowering the flag or when the flag is passing in a parade or in review, all persons present except those in uniform should face the flag and stand at attention with the right hand over the heart. Those present in uniform should render the military salute. When not in uniform, men should remove their headdress with their right hand and hold it at the left shoulder, the hand being over the heart. Aliens should stand at attention. The salute to the flag in a moving column should be rendered at the moment the flag passes.