What are some good ways to prevent birds from from trying to fly through the glass on a window?

In many situations, a window is only used to admit some light in a room rather than to provide a clear view of the outside. ( For example, on some windows the curtains are always kept closed). In that case it wouldn't matter if an anti-bird-strike measure somewhat obscured the view.

Would bird strikes be deterred by the spray-on "snow" that stores put on their windows at Christmas time? How long does that stuff stay on window?

What about simply hanging some lengths of twine over the outside of a window? That could be done in a decorative manner.