Insignia slot

An insignia slot gives an armor piece the ability to support an insignia. As of the May 24th, 2007 update, all armor crafted by an armorer has an empty insignia slot. Collector armor also comes with an empty insignia slot but only if it has less than the maximum armor rating for your profession.

Armor with an empty insignia slot does not have this fact listed in its mouse-over description. However, armor without an insignia slot includes the line "Cannot be upgraded with an insignia" in its description.