"Cult of the Vault" is a challenge from Tiny Tina's Assault on Dragon Keep DLC
The First symbol is found on The Blacksmith's Cottage. Look at the Southwestern corner of it. There you will find the symbol.
The Second Symbol is found in Blood Tree Camp. Get over to the elevated Eastern portion of the Village and look at the First hut's Southern wall to find the second symbol.
Ranks and Rewards
Badass Ranks: 5