I was confused by the clown face at the far left. Does it have anything to do with 9/11? Did someone just paint it on top of the memorial mural? I checked Street View, and the clown is there in the oldest photo, which dates back to October 2007. If it were an act of vandalism, you'd think someone would have painted over it in all the years since.
It turns out that it's the logo of the Fun House, a disco club that was open from 1979 to 1985 on West 26th Street in Manhattan. The place was popular with young people from here in Sheepshead Bay as well as several other outer-borough neighborhoods. Joe Indart, the guy who created this and many other southern Brooklyn 9/11 murals we've come across, had apparently painted a Fun House mural at this street corner before 9/11 ever happened. So, it would seem, what you see above is simply a combined memorial to the loss of lives and the loss of youth.