I have a number of postcards with this stamp on them. No stamp, nothing written on the back of these. I am not sure if it was a stamp used by the post office at the time or if it was just a stamp added by the party selling the postcards. The postcards are all related to World War I. All black and white. All stamped with this, despite having different topics.
"Groupement des Evacues Meusiens" translates to "Group of Meusian Evacuees".