Related Rule
Germany
Practice Relating to Rule 106. Conditions for Prisoner-of-War Status
Section A. Distinction from the civilian population
Germany’s Military Manual (1992) provides:
Combatants are obliged to distinguish themselves from the civilian population while they are engaged in an attack or in a military operation preparatory to an attack. In accordance with the generally agreed practice of states, members of regular armed forces shall wear their uniform. Combatants who are not members of uniformed armed forces nevertheless wear a permanent distinctive sign visible from a distance and carry their arms openly. 
Germany, Humanitarian Law in Armed Conflicts – Manual, DSK VV207320067, edited by The Federal Ministry of Defence of the Federal Republic of Germany, VR II 3, August 1992, English translation of ZDv 15/2, Humanitäres Völkerrecht in bewaffneten KonfliktenHandbuch, August 1992, § 308.
Germany’s Soldiers’ Manual (2006) states:
Combatants are all persons who may directly participate in combat operations, e.g. the members of the armed forces as well as militias and volunteer corps forming part of the armed forces.
Only combatants are entitled to take part in combat operations and cannot be punished for doing so. In contrast, other persons, e.g. mercenaries, can be punished.
If combatants fall into the hands of the enemy, they become prisoners of war.
They may not be held responsible for their participation in permitted acts of war. Violations of international law, however, may be punished according to the law of the detaining power. 
Germany, Druckschrift Einsatz Nr. 03, Humanitäres Völkerrecht in bewaffneten Konflikten – Grundsätze, Erarbeitet nach ZDv 15/2, Humanitäres Völkerrecht in bewaffneten Konflikten – Handbuch, DSK SF009320187, Bundesministerium der Verteidigung, R II 3, August 2006, pp. 2, 3 and 7.