What applies with this traffic sign?

You answered correctly. This traffic sign is a mandatory direction sign indicating that you must turn right. According to German traffic rules, when you see this sign, you are obliged to signal your intention to turn right before doing so. You are not allowed to continue straight or turn left; the only permitted direction is right. So signaling the right turn and following only that direction are both required for compliance with the traffic regulation. This ensures safety and clarity on the road for all drivers.