Related Rule
Practice Relating to Rule 6. Civilians’ Loss of Protection from Attack
Section C. Situations of doubt as to the character of a person
The Report on the Practice of Nigeria states that a presumption of civilian character is held in case of doubt. It adds that during the Nigerian civil war, “the Federal Forces in situations of such doubt did not off-handedly indict or take away individuals of such doubtful civilian character”. They subjected such individuals to a test, in order to determine
the degree of hardness of … their fingers used in handling the trigger. Those found with hardened fingers were presumed to be soldiers (combatants). Although this is an unscientific method of identification, it nonetheless shows that Nigerian practice does not prima facie attribute the status of combatant to individuals of doubtful civilian character. 
Report on the Practice of Nigeria, 1997, Answers to additional questions on Chapter 1.1.