Hi Caz, I'm afraid treatment of U-boat Pow's is not a subject I have researched in any depth. My understanding is all were searched for any thing of anything that of interest, and I guess like all the forces involved in the conflict had some who took some items illegally, as shown in the various items available on sites like E-bay etc. You say have some initialled, therefore the U-boat archive should be the way to go to find the original owners. Good hunting, regards John