3 tips for using decals and paint on windows to prevent bird strikes
1. Use multiple decals; create a pattern that covers the window uniformly. Elements arranged in columns should be four inches apart. Elements placed in rows should be two inches apart. This is often called the 2 x 4 Rule.
2. Elements should be at least one-eighth inch in width and should contrast as much as possible with the windowpane.
3. Patterns can be placed on the inside or outside of a window that is transparent. If it is reflective, the pattern must be applied to the outside.
Source: Fatal Light Awareness Program (FLAP)