Who must signal a change of direction here?

In this situation, only the motorcycle rider must signal because they are changing direction to the left. You are driving straight ahead and do not need to signal. In German traffic, signaling is required whenever you change direction, such as turning left or right, but not when going straight. Correct use of blinkers clearly communicates your intentions to other road users and helps prevent accidents. So, answer 1 is correct—only the motorcycle needs to indicate here.