I am sometimes asked about the magnet with a star on the back of my car.  Nope, its not that my husband got promoted to General....  It is a Blue Star Service Banner, and it does signify that my husband is deployed to a combat zone.

The Banner originated in WWI, in Ohio, and quickly became the symbol of a child in service overseas.  World War II saw official rules for the banner approved by the Department of War, and the Department of Defense in 1967 implemented the rules that govern the display of the banner today.  Although the banner saw a decline in use over the last few decades, it has been embraced as a symbol of pride among those families with loved ones serving in Afghanistan and Iraq.

The banner is only authorized to be displayed by immediate family members of a member of the armed forces (defined as:  wife, husband, mother, father, stepmother, stepfather, parent through adoption, foster parents who stand or stood in loco parentis, children, stepchildren, children through adoption, bothers, sisters, half brothers, and half sisters) and only for those servicemembers who are deployed to a combat zone.  (Another version of the banner is authorized for display by companies or organizations with such members.)

Although it is more rare today, families that have multiple members deployed can get flags with up to 5 stars, one for each member in service overseas. 

When a banner is displayed with a gold star in place of the blue, it signifies that the family member has died in service.

For more information on the history of the banner, the American Legion is a great resource.  They also have service banners available for purchase, as well as lapel pins, which are also authorized by the Department of Defense.  The official rules for display can be found here.

For mothers of servicemembers currently deployed overseas, the Blue Star Mothers is an active organization available for support.