What is this checkered pattern on the rear window of the car? I see it on many (but not all) cars, in wet conditions. Sometimes it has a light rainbow pattern to it (similar to oil spilled on water, so mostly violet shades). I don't think I ever saw it in dry and sunny weather. Sometimes the pattern is diagonal and with slightly larger "tiles", probably depending on the car or its window.
That is an artifact of the manufacturing process. The coating is sprayed on by the glass manufacturer and what you see a slight difference in the thickness of the application due to the way the spray lines overlap.
If you look nearly all vehicles with tinted windows will show this and it's often more visible with polarized sunglasses on (in my experience) than without.
From what I could find, this is an artifact from the manufacturing process.
These start as a flat sheet and are "bent" into final shape. The subsequent cooling (annealing) by cool air nozzles leave internal stresses into the glass, which is what you can see. These also act as "guides" for fractures in case of an accident, causing the piece to fragment in a somewhat predictable way.
Here is a link to a previous answer to this question:
And a "How it's made" video: