This is one of five quests where your goal is to cut down Brencis's banner hanging from one of the city gates - in this specific case, the South Gate. This quest will appear in your journal when you approach the city gate. Completing all of these quests unlocks the "Capture the Flag" achievement.
Time Segments: 1
There is a banner of Brencis's regime waving above the South Gate. Maybe someone should take it down and show people that the fight against the vrakhiri has started?

1. Get inside the gatehouse
I need to find my way into the gatehouse so I can pull down the banner.
You must reach the room located above the entrance gate of the tower. You can do this either at night or during the day. During the day, you must find scaffolding to reach the city walls, which you can then cross to enter the room.
In this case, you can find the scaffolding near the walls, inside the city, a bit further west of the south tower. The same scaffolding will allow you to get to Dragosti's tower.

Then head back to the tower, this time along the walls.

2. Defeat the guards
Of course the guards won't stand idly by while I pull down the banner. I have to get rid of them first.
Take out all guards who stand in your way and attack you.

3. Pull down the banner
With the guards gone, the only thing left to do is pull down the banner.
Once you get rid of the guards, approach the wooden structure inside the gatehouse and cut the ropes holding the banner. Reward: 100XP

4. Ending
I was able to pull down one of the vrakhiri banners at the South Gate. Maybe it will bring hope into people's hearts...