What do these traffic signs indicate?

You correctly identified that the signs indicate "No entry 100 m ahead."

In German traffic rules, the circular red sign with a white horizontal bar means "No entry" from the direction you are approaching. The additional rectangular sign below it indicates the distance to this restriction. So here, the no-entry zone starts 100 meters after the sign.

This means you are allowed to continue for 100 meters, but then you must not enter the road or area beyond that point. This advance warning gives you time to prepare to stop or take an alternate route.

Remember, the sign itself is a prohibition sign and always warns about a restriction starting at or after the indicated distance. It does not indicate a duration, length, or type of road (e.g., one-way street).