June 14 is Flag Day, one of six days each year that Postal Service facilities are required to fly the POW-MIA flag.
The flag honors the sacrifices made by members of the armed forces held as prisoners of war or listed as missing in action.
The POW-MIA flag must fly below the U.S. flag.
For additional information, refer to the Postal Service’s guidelines on U.S. flag display and maintenance, as well as the requirements for displaying the POW-MIA flag.
Source: USPS News Link