All persons present should face the flag, stand at attention and salute on the following occasions:

1. When the flag is passing in a parade or review. The salute to the flag
in the moving column is rendered at the moment the flag passes.
2. During the ceremony of hoisting or lowering the flag.
3. When the National Anthem is played and the flag is displayed.
4. During the Pledge of Allegiance … I pledge allegiance to the flag of the United States of America and to the Republic for which it stands, one Nation under God, indivisible, with liberty and justice for all.

from Flag Co