May 30 is Memorial Day, one of six days each year Postal Service facilities area 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.
Facilities that are open on the holiday must fly the U.S. flag at half-staff. The POW-MIA flag must fly below the U.S. flag.
The U.S. flag must be flown at half-staff from sunrise — or the hour when it’s raised — until noon. Then, hoist the flag to the peak of the staff, where it either must fly until the time of closing or no later than sunset (unless the flag is lighted).
Facilities that fly the flag at all times and are closed on Memorial Day should lower the flag to half-staff when the facility closes prior to the holiday. Return the flag to full staff when the facility opens Tuesday, May 31.
Source: USPS News Link