I will admit—my first thought when I saw this was “wow, that’s… ugly.”
Turns out it actually has an interesting story, though.
They did some digging and found New Providence, NJ.
New Providence, which is only about an hour out of New York City (40 minutes if you catch the express!), is a heavily residential town chock-full of people who commute to New York daily. As such, back in 2001, it was heavily affected by the bombing, and apparently lost quite a few residents.
Flower Mound showed its honor for the families affected by the tragedy by donating an eight-foot-square granite memorial. The illustration was designed by a couple of middle-school twins.
New Providence was deeply touched by the gesture, and the memorial is featured prominently in Centennial Park.