In the Spring we get indignant and furious robins throwing themselves at the windows and pecking at their reflection, particularly in the mornings. I can watch them from a few feet away, and they don't seem to see me, presumably because they are seeing quite a convincing reflection of themselves and the garden.

I think the most effective deterrent for kamekazi attack is something on the OUTSIDE of the window, as the reflection would hide things stuck on the inside.

Something like the shading used on greenhouse glass might make all the difference to the apperance of the window, and it sticks fairly well but is removable.