What must you do upon seeing this traffic sign?

This traffic sign indicates a pedestrian crossing (Zebrastreifen). According to German traffic rules, when you see this sign you must:

1. Approach at a moderate speed if it is clear pedestrians want to cross. This means you should be prepared to stop and be attentive to pedestrian movements.
2. Allow pedestrians to cross the road. Pedestrians have the right of way on zebra crossings.
3. Not remain stationary on the pedestrian crossing if traffic backs up behind you. You must keep the crossing clear so pedestrians can safely cross and avoid blocking their right of way.

These rules ensure pedestrian safety and smooth traffic flow near crossings. Always be alert and give priority to pedestrians at these signs.