What collar device signifies the rank of Colonel?

The rank of Colonel is signified by a silver eagle collar device. This symbol is well-established in military insignia, where the silver eagle represents the rank of Colonel, which is typically above Lieutenant Colonel and below Brigadier General. The eagle's design indicates the level of authority and responsibility held by the officer in the military hierarchy.

The other options presented do not represent the rank of Colonel; for instance, a silver oak leaf is used to denote the rank of Major, while a gold oak leaf signifies a Lieutenant Colonel. The choice of "None" does not apply since the appropriate insignia does exist and is recognized within military standards. Understanding these insignia helps in recognizing ranks and the corresponding responsibilities in military settings.