It's a reference to a 1963 episode of "The Twilight Zone," in which Shatner's character sees a gremlin on the wing of the plane. The triangles signal to the crew which windows have the best view ...

"Before take-off I was looking out my window and noticed what looked like a piece missing from the wing. It turns out, it is just a cosmetic issue and doesn't effect the plane, but it startled me.