Postal Service facilities that are open Sundays should fly the U.S. flag at half-staff on Sunday, May 7, which is National Fallen Firefighters Memorial Service Day.
USPS facilities that fly the flag at all times and are closed Sundays should lower the flag to half-staff when the facility closes prior to National Fallen Firefighters Memorial Service Day. Return the flag to full staff when the facility next opens for business.
To fly the flag at half-staff, hoist the flag to the peak for an instant and then lower it to the half-staff position. The flag should be raised to the peak again before it’s lowered for the day.
The USPS Administrative Support Manual has guidelines on U.S. flag display and maintenance.