Also for deer. Deer are idiots, the males even more so during the rut. They will see similarly-sized deer in any vertical glass surface (their own reflection) and charge the window antlers-first. They break through the glass and now you have a deer running around inside your house or school. A few stickers won't stop them from seeing their reflection, but it will put an "object" between them and thereby stop the charge. I've even seen this in car windows. Tall deer (elk) are so dumb that they will repeatedly charge the tiny elk reflected in a car window. They aren't attacking the car but the other elk they think is inside. I'm surprised they all don't drown every time they see rival elk inside a calm lake.