Emblems of the United States Air Force

United States Air Force unit emblems have their origin in four different types of insignia used since the early twentieth century by United States Army units. Although the Army continues to distinguish among the different types of unit insignia it uses, the Air Force describes them all as “emblems.” Air Force unit emblems may be of one of two differing shapes, a disc or a shield of a prescribed shape.

Source: Wikipedia — Emblems of the United States Air Force (CC BY-SA 4.0)