What does this traffic sign combination indicate?

The combination of signs means that you must prepare to stop at a STOP line or stop sign 100 meters ahead. The top sign alone is a "Give way" (yield) sign, but the additional sign indicates that a full stop is required shortly ahead, not just yielding. This means you must slow down and be ready to come to a complete stop at the STOP sign that is 100 meters away. Always obey the upcoming STOP sign to avoid accidents and follow German traffic rules precisely.