The Flag of the United States of America is one of the oldest national standards in the world - older than Great Britain's Union Jack or France's Tricolor.
The United States of America Flag should be displayed on all days, especially on:
New Year's Day - January 1st
Martin Luther King, Jr. Day - 3rd Monday in January
Lincoln's Birthday - February 12th
Washington's Birthday (Presidents' Day) - 3rd Monday in February
Easter Sunday - variable
Mother's Day - 2nd Sunday in May
Peace Officers Memorial Day (half-staff) - May 15th
Armed Forces Day - 3rd Saturday in May
Memorial Day (half-staff until noon) - last Monday in May
Flag Day - June 14th
Independence Day - July 4th
National Korean War, Veterans Armistice Day (half-staff) - July 27th
Labor Day - 1st Monday in September
POW/MIA, Recognition Day - 3rd Friday in September
Constitution Day (Citizenship Day) - September 17th
Columbus Day - 2nd Monday in October
Navy Day - October 27th
Veterans Day - November 11th
Thanksgiving Day - 4th Thursday in November
National Pearl Harbor Remembrance Day (half-staff) - December 7th