Hold a lighter up to a double-glazed window and count the flames you see in the glass.
You'll see four reflections, one from each glass surface. If all four are orange, it's plain glass. If one is violet, blue, green or pink, that surface carries a low-E coating: a thin metal layer that keeps heat in and sun out.
It also keeps radio out. Measurements through low-E glass run from 10 to 45 dB, typically 30 to 40 dB.
That's the new office building where nobody gets a cell signal, and the outdoor AP that can't reach the room behind the window. Tinted glass isn't the same thing, and the flame test tells you which one you have.
Keep the flame brief, and away from blinds and window film.
How many of the windows around you are coated?