When must you wait at this traffic sign?

This traffic sign is known as a railway crossing sign (Andreaskreuz) in Germany. It indicates that you are approaching a level crossing with no barriers or gates.

You must wait in the following situations:
1. When a railway employee is waving a white-red-white flag, signaling that a train is coming or the crossing is not safe to cross.
2. When you cannot cross the level crossing without stopping on it—meaning if traffic or other reasons would force you to stop on the tracks, you must wait.
3. When a rail vehicle (train, tram) is approaching the crossing.

The key rule here is to never stop or wait on the tracks and to only cross when it is fully safe and allowed. Observing these signals and rules prevents accidents at these dangerous crossings.