Sometimes a subject doesn't need to be as apparent for a photo to be successful. I'm not sure that this photo has a definitive subject. I think if you asked 10 people to tell you what this photo is about, you'd probably get a few different answers.
Does a photo need to be about something or have an obvious subject to be successful? I would have said yes not too long ago, but I am softening on that stance a bit. I still think my best work generally has simple and compelling subjects, but I feel there is room for shots like this one.
There are more questions here than answers, and I think that intrigue is what makes this shot appealing.
One question I had to answer was why I photoshopped the sign upside down. It's interesting that the person assumed that I manipulated the sign to add interest instead of assuming that I took the shot because I though the upside down sign was interesting, which was the case.
This style of photo that focuses on shape and composition is something that I have been working on regularly, and will become a new theme in my work as I start to move through material more often on this site. It will be a nice departure from the rest of my work, and a great way for me to introduce new ideas into my work.