Who is required to indicate a change of driving direction here?

You have correctly identified that all three—yourself, the red car, and the motorbike—must signal their intended change in driving direction.

According to German traffic rules, any driver who intends to change direction, such as turning left or right, or changing lanes, is required to use their turn signal to inform other road users of their intentions. This is important for safety and to avoid misunderstandings on the road.

In the image, you (1) are turning left, the red car (2) is turning left, and the motorbike (3) is also turning left. Therefore, all three drivers must indicate their change of direction with the appropriate turn signals before executing the turn.

Remember this rule for future situations: Whenever you change direction or lanes, always signal early and clearly to alert others and maintain safe traffic flow.