I noticed that many windows have this kind of sun limiter at the edges and wondered what exactly they are.
The black dots blend the border into the glass A: Windshield glass contains a black enamel band (called the frit) around the periphery that is baked into the glass. This black band includes a border of dots. See figure. The band has an etched surface to enable adhesive to bond to the glass, says a sales manager at Able Auto Glass. When car manufacturers install the windshield, they bond the windshield to the vehicle with adhesive placed on the etched part of the black enamel glass area (inside surface). The outside of the enamel band shades the adhesive from the Sun and protects it from ultraviolet radiation. The band also serves a cosmetic purpose by covering up the adhesive and gives the windshield edge "a more finished look."