A geometric pattern or construction. Maybe a golden spiral. Or something that looks like it's out of Da Vinci's notebooks.
A map, or a star map.
A perspective drawing with very obvious foreshortening.
Something based on the allegory of the cave or the divided line of Plato? The latter probably wouldn't stand without explanation, though.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.