The Great Vault is home to a number of possible rewards in World of Warcraft: Shadowlands. If you’re completing Castle Nathria raids and Mythic+ dungeons throughout Shadowlands, you’re eligible to receive high-value items from the vault, but there’s one item you might be lacking when you go to claim your prize.
The Ancient Insignia is attached to a quest, also called The Great Vault. This will not appear until you have completed the entire storyline for Torghast, concluding with The Weak Link, where you break the Runecarver free of the chains that bind him to The Maw. This is also the final quest before you can start earning legendary memories.
Once that’s complete, you can speak to Ba’vol in the ring of Fates, housed within the central hub of Oribos. The quest is simply to open The Great Vault, which you can do after you’ve earned a reward from completing one of the vault’s requirements. You’ll then need to wait until after the weekly Tuesday reset before you can open The Great Vault to pick your reward. The Ancient Insignia will come with it.
After picking out your loot, return to Ba’vol, and let him know you have finished making your selection. Hand over the insignia, and you can complete the quest for a bit of XP and some gold.