This photo was taken on RyanAir flight from Portugal to the UK in May 2010. Author says that he didn’t notice the dark spot in the upper left of the image along the curvature of the Earth when he took the photograph.
Click on the photos to enlarge.
source: www.meetstheweird.com
First decent photo of TR-3B
Its a plastic separator between the two planes of plastic/glass.
Polarized windows do not have "separators" in them.