This is a reference to the American Gold Star mothers, an organisation founded after the First World War to help mothers who had lost children in the war.
It became a tradition for families to hang a Service Flag in their window, with a star for each family member serving in the military. Those who were alive were represented by a blue star, while those who had perished were represented by a gold star.
The group still exists today, with membership open to any mother who has lost a child in service of the United States. The group is strictly non-political. On the last Sunday of September, the United States honours Gold Star Mother's Day.