As parrot owners, we greatly underestimate the importance the monthly home touring with our parrots. The majority of us are changing, adding or removing things from our homes if not weekly, for sure monthly. Touring your home with your parrot may seem senseless, but those who do find that their parrots 'spook' less often and avoid windows, mirrors and stairways then those who do not. Its kind of like reading to your parrot, we all do it with a new arrival, but it is just as important with the parrot that has been with us for years.
Window decals, as mentions by others, is a great tool in denoting windows and mirrors. NOTE: A decal of a 'Bird' in flight is far more effective then one's favorite football team. Color or plain black seems to have little if any affect, but the color decals just look better in most homes. They also get less notice or at least positive notice by visitors.
Ultra clean glass, whether its windows, doors or mirrors is more difficult to define for humans and parrots alike. The decals we use have saved me more often that I would want to admit. This is very true when like a glass door it can be either open or closed.
Will the decals fully assure that your parrot will not from time to time fly at the glass surface? NO. But, even a split second awareness can change a head on crash into a side swipe.