Warns you to equip your PvP trinket before combat begins with Archimonde, and reminds you to unequip it when the boss dies. Will warn you even if you don't target the boss before pulling.
Be sure to bring either the epic or the non-epic Medallion in your bags, not both.
FYI: The equip warning will trigger again when you unequip your trinket after the boss dies, until you leave the area.