Hilarious but illegal

As I was driving North on I-15 this morning, I looked to my left and noticed a train. As usual, my eye caught on the graffiti all over the cars. I came upon a car that had the Union Pacific symbol on it, and underneath their motto "We will deliver". Underneath that, in spray paint, someone had written "But when?" Yah, that got me to laugh right out loud! I don't typically support illegal activities. In fact it is my job to 'cure' adolescents from committing crimes. But this one was really clever. Hysterical really! So if someone has defaced property, but they do it very cleverly, does that make it illegal still?