A Symbolon

A Symbolon is a side quest in Dragon Age II Mark of the Assassin DLC available if you bring Bethany as one of your companions.

''An unusual bird feather has been found. See if there are more.''

Acquisition
This quest appears in Chateau Haine. There will be a door on the opposite of the alcove where the cook is, leading to a small room containing a lootable chest and a painting. Taking the painting will start the quest.

Walkthrough
There are a total of three paintings you need to find.

1. Chateau Haine - In a room opposite the alcove where the cook is.

2. Chateau Haine - On a small table, in the same room where you can find the Codex entry: Uncertainity

3. The Dungeons - Close to the crack in the Wall that leads to The Retreat, there are four old cells. The final painting is located in the cell on the northwest (upper right cell, facing north of the map).

Result
Once the third painting has been found a treasure cache will be marked on the map. Its location is found in The Retreat, on the left arm of the crossroads after you first see a pair of fleeing Ghasts.