A relative of Jean Krans asked me if I knew what kind of badge it is. The idea of the French Foreign Legion is based on this sentence from the wikipedia site:
"Hij noemde zich voortaan Jean en droeg dageljks het insigne van de franc-tireurs, een gouden doodskopje, als dasspeld onder zijn kin."
Roughly translated:
From now on he called himself Jean and wore daily the isignia of the Franc-Tireurs (a golden skull) as lapel pin under his chin.
I have no further thoughts about the badge because it is not my area of interest, I'm just trying to help someone solving a mystery.