A roundel is a circular disc used as a symbol. The term is used in heraldry, but also commonly used to refer to a type of national insignia used on military aircraft, generally circular in shape and usually comprising concentric rings of different colours. Other symbols also often use round shapes.
Hawker Hurricane showing a Second World War-era Royal Air Force roundel
A cockade is a knot of ribbons, or other circular- or oval-shaped symbol of distinctive colours which is usually worn on a hat or cap.
A woman fastening a red-and-white cockade to a Polish insurgent's square-shaped rogatywka cap during the January Uprising of 1863–64
Charles Edward Stuart wearing a hat with a white (Jacobite) cockade
John of Austria wearing as a brassard the red cockade of the Spanish armies
General André Masséna of the French Revolutionary Army wearing a bicorne with a tricolor cockade