[carlmu]

Thanks for the answers!
The plate was photographed and then unfortunately removed from the wreck last week, after 69 years in the open, and snow covered from October to June!
The guy who took the picture tells me that the plate measured ca 3x5 cm and was fastened towards the edge of a reasonable big part of the fuselage and near to or at the other side of some hinges. He thought it might have been a door or covering of some kind.
This part must have been retrofitted, becuase the plane was manufactured in the fall 1940 while the Weserflug part was produced i February 1941.
Does this info give a clue?