"Cult of the Vault" is a challenge from Tiny Tina's Assault on Dragon Keep DLC
The First symbol is found by finding this long rope running from nearby the Streetwise Wharfs toward the building in the center of town.
The Second symbol is found in the central part of Flamerock Outskirts. Look for the building just South of the hole in Flamerock. Go to the Northeastern part of that building to get at it.
Ranks and Rewards
Badass Ranks: 5