What applies in the area 15 m in front of and behind this traffic sign?

You were right with answers 1 and 2.

This sign marks a bus/tram stop. In Germany, a special protection zone applies: in the 15 m area in front of and behind the stop sign, you may stop briefly, but only if you do not obstruct public transport or passengers. That’s why “stop” is allowed, but only under the condition that boarding/alighting is not hindered.

Parking is not allowed in this 15 m zone. The rule is meant to keep the stop area free so buses can pull in/out safely and passengers have space and visibility.

Rule of thumb for similar questions: at bus stop signs, stopping can be permitted for a short moment if nobody is hindered, but parking is prohibited within 15 m before and after the sign.