Displays the normal sigil icon when you have Sigil of Awareness equipped. When you swap to Sigil of Virulence the internal cooldown is shown. When the "Unholy Force" 200 strength buff procs the icon is highlighted indicating you should swap back to Awareness. Combo this with a macro to swap between Sigils on keypress.
/equip Sigil of Awareness
/equip Sigil of Virulence