SPRAY - Ongoing

The artwork in the ongoing Spray series focuses on concepts of legality in regards to graffiti.  All of the pieces in this series were born of illicit actions in subway tunnels deep below the ground and inside metro depots guarded by security and surveillance cameras. Walls were scaled and traps were opened to create these works. It is safe to say that the act of graffiti and many of the acts surrounding graffiti are illegal, but should the works in this series also be identified as illegal?  The paint on each of these works was not sprayed directly on a metro carriage, but rather on a circular metal canvas temporarily adhered to a metro carriage.  A metal canvas belonging solely to the artists. It could be argued that the canvases are a part of the graffiti painted, however as the metal canvases are not property of the city, state, or any other authority who has not given permission to have them painted, can they be considered illegal? Should they be considered part of the crime of graffiti, or perhaps the only part of the graffiti action that was not a criminal act?