Although rarely displayed since World War II, the Service flag can now be seen hanging from the windows of homes with family members serving in the United States Armed Forces.
The Service Flag, also known as the "Son in Service" flag was commonly displayed during World War I and II in patriotic support of our armed forces fighting for freedom. The flag is authorized to be flown during any period of war or hostilities in which the Armed Forces of the United States may be engaged, for the duration of such period of war or hostilities.
In October, 2001, the Department of the Army issued a certificate of authorization to serviceflags.com of Carson City, Nevada, to manufacture and sell the Service flag and Service Lapel button for civilians. Family members authorized to display the flag include wife, husband, mother, father, stepfather, parent through adoption, foster parents who stand or stood in loco parentis, children, stepchildren, children through adoption, brothers, sisters, half brothers, and half sisters of a member of the Armed Forces of the United States.
Each blue star on the flag represents a family member serving in the Armed Forces. The blue star is replaced (or covered) with a gold star to represent a member killed or dies while serving their country during the war or hostilities.
Persons interested in learning more about the Service flag or where to purchase one should visit Service Flags
This information was borrowed from Service Flags