The left hand card has pencilled on the back "RGLI Head Quarters Signallers in France, 1918", and the right hand card just "RGLI Signallers". I've been unable to find out much further information about these men, but I believe they may be some of the surviving members of the RGLI following the massive casualties of April 1918. In his book, Diex Aïx: God help us (1992, p. 24) Major Edwin Parks records that "As a fighting unit the RGLI was finished.... On 27 April, just seven months after they arrived in France, the tattered remnants were posted to Ecuires where they took over from a battalion of the Honourable Artillery Company as guard troops at Haig's headquarters in Montreuil." Could these pictures have been taken there? I'd welcome any further information.