Related Rule
Germany
Practice Relating to Rule 106. Conditions for Prisoner-of-War Status
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 Konflikten – Handbuch, 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.
Germany’s Military Manual (1992) provides that members of a levée en masse “shall be combatants. They shall carry arms openly and respect the laws and customs of war in their military operations.” 
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 Konflikten – Handbuch, August 1992, § 310.
Germany’s Military Manual (1992) states:
Recognizing that there are situations in occupied territories and in wars of national liberation where, owing to the nature of the hostilities, a combatant (especially a guerillero) cannot so distinguish himself from the civilian population, he shall retain his status as a combatant provided that, in such situations, he carries his arms openly:
(a) during each military engagement, and
(b) during such time as he is visible to the adversary while he is engaged in a military deployment preceding the launching of an attack in which he is to participate.
The term “military deployment” refers to any movement towards the point from which an attack shall be launched. 
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 Konflikten – Handbuch, August 1992, § 309
In reply to a written question in Parliament in 1977, a German Minister of State emphasized that the German delegation present during the negotiation of the Additional Protocols favoured the inclusion of a rule imposing a duty on guerrillas to carry arms openly in combat, as well as during the phase preceding an attack. According to Germany, a clear distinction between civilians and combatants was absolutely necessary, even in the context of guerrilla warfare. 
Germany, Lower House of Parliament, Answer by Dr. Hamm-Brücher, Minister of State, to a written question, 13 May 1977, Plenarprotokoll 8/27, 13 May 1977, p. 1985.
Upon ratification of the 1977 Additional Protocol I, Germany stated:
The criteria contained in the second sentence of Article 44, paragraph 3, of Additional Protocol I for distinction between combatants and the civilian population are understood by the Federal Republic of Germany to apply only in occupied territories and in the other armed conflicts described in Article 1, paragraph 4. The term “military deployment” is interpreted to mean any movements towards the place from which an attack is to be launched. 
Germany, Declarations made upon ratification of the 1977 Additional Protocol I, 14 February 1991, § 3.