Birds fly against the window (Public/commercial building)

Bird Protection Glass is glass with a UV-reflective coating. It isn't visible to people but is visible to birds. 

Ornilux is a brand that is well-known for their bird protection glass and is what the Philadelphia Zoo uses as their primary method of stopping birds from fatally colliding with their windows. 

This solution is more sensible for commercial businesses and office buildings than residential homes due to the costs. However, once installed it is a very effective solution! 

There are special reflective decals that only birds are able to see and there is also standard mylar tape and stickers from any craft store that can be purchased and applied to the interior of the windows. 

Amazon carries a good selection including a wide variety from the top-rated Window Alert brand. For example check out this one.

Attach a window screen &/or a mesh-like netting a couple inches away from the outside of the window. This will stop the birds prior to impact and will safely bounce them off. 

Home Depot, Lowes, and other home hardware stores carry rolls of special protective mesh that is cheap and effective! 

There is a special film that is applied to the window that is invisible to those inside but from the outside is opaque. 

Amazon carries several variations of window film including Bird's Eye View by Artscape. This film is applied on the interior of the window. For example check out this one.

Another film that has many options available (i.e. tinted, pattern/decor, white, clear, etc.)  and is also applied to the interior of the window is CollideEscape which can be found here.

Keep interior blinds and shades partially closed. This will allow birds to see contrast and realize that the window is not open sky/part of the environment. 

This option would definitely be for those that leave the house during the day and/or don't need the shades open.

Use tempera paint to create a design on the windows. It can be a simple stencil pattern or an actual painting with a subject and background. 

The average homeowner and commercial business (i.e. bank, clothing store, restaurant, etc.) would probably not want to paint on their windows, however, for childcare centers/schools, art studios, bookstores---this would be something a little more suitable.