Executive Order 3360—Official Flag for Secretary of State
The White House, November 28, 1920.
Whereas it frequently devolves upon the Secretary of State in virtue of the statutory authority conferred upon him to perform public acts of foreign intercourse under direction of the President;
And whereas it is proper that in the performance of such ceremonial acts as the representative of the President, it is appropriate his representative function be designated by an appropriate flag, to be displayed when occasion may require;
Therefore I, Woodrow Wilson, President of the United States, do hereby direct and prescribe that an Official Flag, indicative of the office of Secretary of State, be prepared as follows:
The ground or field of such flag to be dark blue with the arms of the Department of State in white charged upon the center, and with a gold star on each side of the arms.
And I further direct that on the approaching ceremonial visit of the Secretary of State to certain States of South America, the above prescribed flag shall be displayed on the national vessel which conveys him, so long as he shall be on board the ship, and upon the launch which may convey him to the shore when his communication therewith becomes necessary in the discharge of the public mission with which he may be charged.
Woodrow Wilson, Executive Order 3360—Official Flag for Secretary of State Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/350386