Rick told me that the black band around the edge of the glass is called “frit,” a baked-in ceramic paint that’s essentially impossible to scrape off. That frit band along the edge of the glass, he told me, serves three main purposes.
Most importantly, it acts to prevents ultraviolet sun rays from deteriorating the urethane sealant. That matters, because the sealant doesn’t just keep rain out of the car, it actually holds the glass in place. The last thing you want is the sun to cook your adhesive, and send your window flying out the next time you hit a speed bump.
The frit band also acts to provide a rougher surface for that adhesive to stick to, and it’s a visual barrier, preventing people from seeing that nasty glue from outside.
Rick told me that auto manufacturers used to use gaskets to keep windows sealed from the elements, and over top of that gasket, they’d fasten chrome trim to prevent the windshield from rattling out. In the ‘50s and ‘60s, as auto manufacturers began transitioning from metal trim to adhesives to hold the glass in place, a way of protecting the glue and ensuring good adhesion became necessary, and eventually the frit band became standard on essentially all automotive windshields.
“So there you go: the dots on the edges of your windows are there to provide a smooth transition from that crucial solid black frit band in order to prevent distortion and to look more aesthetically pleasing, while the dots behind your rearview mirror keep the sun from your eyes.”