A salesman told me they are to cut the sunlight. Since that area is pretty much obscured by the rear view mirror anyway I guess it could make sense that, to increase contrast with the images in the mirror, you wouldn't want the sun shining brightly around the mirror.
Not sure what that is either BUT I do know NOT to put a toll transponder on them. They tell ya to put it behind the mirror so I did as I always have and the 'scanner' couldn't read the bar-code through the dots.
Those dots have been on front and rear windshields of most cars today. They are also on the rear side windows of trucks and suv's. I believe their primary purpose is to hide the seals and back side of the trim inside the car so rough edges cannot be seen. On the pilot the do extend down to the mirror, which helps block out direct sunlight behind the mirror. They would have to be conductive, and connected together to act as any kind of an antenna. One of the rear windows has a wire laminated inside the glass. That is the antenna.