What must you do when you see this traffic sign?

Your answer is correct. This traffic sign warns of a sharp left bend ahead. According to German traffic rules, you must reduce your speed before entering the bend to maintain control and safety. Additionally, you should keep as far to the right as possible to stay in your lane and allow vehicles coming from the opposite direction enough space. Indicating left before the bend is not required because the bend itself is part of the road, not a turn or exit. Understanding this helps you drive safely through bends and anticipate road conditions.