Some lines in the New York City subway system use diamonds and circles to differentiate between express and local, respectively. This is the case on the 7 (Flushing) line as well. However, I while most trains simply carry the appropriate sign, the trains on this line used lights instead, creating a unique effect:

As far as I know, this is only line which features these lights. The picture above illustrates the green circle representing the local train. Below is a red diamond representing the express:

I was not particularly happy with the second photo, but it does illustrate both the red light and an interesting side-effect that I observed: the reflection of these bright colored geometric lights on the windows both from other trains and within the car itself. I found myself watching the colored shapes dance, and contrast with a few of the passengers sitting in the car or rushing along the platform. Not mesmerized per se, the way a cat reacts to a light pointer, but still focused. I don’t know if anything will come of it besides this brief post.