A few years ago, Banksy engaged in a 30 day residency in New York. Each day offered a new work or performance. It was all ephemeral as street art tends to be. One piece remains visible from the residency.
The streak of red on the boy's forehead and the flash of light under the hammer are reflections on the protective sheet of plexiglass covering the work. Many of Banksy's pieces from the residency were protected with plexi, or roll down metal gates before being removed. One piece, Geisha is still behind its protective gate, but it might as well be elsewhere.
The boy with the hammer was protected by Saul Zabar, of the Zabar's across the street. He is genuinely fond of the work and wants everyone to enjoy it. Still it seems so strange to have street art protected by plexiglass. It is maybe a little poignant.
For more about Bansky's work, check out this awesome page: