Final answer:
The unit insignia of the US Army Special Forces should be centered on the flash of the Green Beret, the signature headgear of this elite commando group established during President John F. Kennedy's era.
Step-by-step explanation:
The insignia that should be displayed, centered on the flash of the beret, especially in the case of Green Berets, is the unit insignia of the US Army Special Forces. The Green Berets are members of the US Army Special Forces, a group known for their distinctive headgear as an integral part of their military dress uniform. As elite commandos, the Green Berets were established with the hope, notably by President John F. Kennedy, that they could execute special missions to potentially avoid deploying larger military units into combat.