I've had it around since I was a kid but I didn't know what it was until recently.
KR.GEF.LAGER. as I found out is abreviated German for KRIEGSGEFANGER LAGER - translated as WAR PRISONER CAMP.
THORN refers to the location in Poland of Stalag XXA, and NR. 14275 was my grandad - Private Walter Grant. Royal Army Ordnance Corps.