RE: Pfalz DIII resources -- Photos, Drawings, Plans, etc.
I believe one of these rectangles is rigging instructions in a celluloid pocket. This appears to have been standard practice on the German side during WWI. I've always wondered just what was written on them. It seem probably that someone over on the Aerodrome forum has this information.
The other rectangle is almost certainly the aircraft identification tag. Again, I'm not aware of details.