There is much contrast between the major shapes in this photograph. I would have to describe it as abstract, because I can’t realistically tell what it is that I am looking at. Perhaps it is some sort of door hinge, but it is difficult to tell because it looks like there are bricks behind the light blocks and the bricks look far away, however the rectangular blocks also appear to be on the same plane. Visually, it is difficult to tell what Siskind captured in this shot. There is a lot of texture in the rectangular shapes; it looks like peeling paint or rusting metal.
Good description. I’m thinking it might be a building and those are plastered/blocked windows, but I don’t know either.