What Are Blue Star and Gold Star Military Families?
Flying Flags in the Window
The white field, edged with red, can hold up to five blue stars. The blue of those stars symbolizes hope and pride for the service of a family member. The flags are displayed facing out in a front window. Silver stars, which indicate a family member wounded in action, symbolize gallantry, while gold stars, added for family members killed during active duty, stand for sacrifice made for honor and freedom. The gold or silver stars are made slightly smaller than the original, so that a thin border of blue shows around the addition.
Entitlement to Flags
Flying blue-star flags is limited to specific family members. The spouse; parents, including adoptive or stepparents; siblings; and children, whether natural-born, adopted, foster children or stepchildren, are entitled to display the window flags.
Source...