A service flag may be displayed in a window of the home of the immediate family of a person serving in the Armed Forces of the United States during any period of war or hostilities:

 

During the 1^st & 2^nd World Wars, mothers would hand-make flags and post them in their front windows.  Each flag had a white background, a red frame, and a star for each family member in the armed forces.

 

Blue Star—A blue star was centered on the flag for each member of the family in the armed forces.  (If the mother had 3 sons and 1 daughter in the army, 4 blue stars would be posted.)

 

Silver Star—A smaller silver star would be placed atop a blue star for each family member injured in the armed forces.

 

Gold Star—A gold star covers a blue star when a family member is killed or dies while serving.

 

On 1 December 1967, an Act of Congress officially recognized and defined the design and use of service flags.

 

Families are once again displaying the service flags.  Organizations may also display a flag when members join the military (special design specifications should be followed.)--Information from US Archives