Adjacent non-supplementary angles

This is an arrow. Arrows are used today for many reasons. Arrows are used on signs to point which way to turn. Arrows are used on maps to point out specific locations. Arrows pointing to something are used to emphasize it. But, arrows also show adjacent non-supplementary angles, because they have two angles that share a side and a vertex, and because an arrow needs to point to something, the head does not form a flat line, because then it would not indicate a direction. This particular image was found through google images, using the URL http://www.designofsignage.com/application/symbol/hospital/largesymbols/arrow-down.html.