One of the memorable things we did when in London this past summer was to visit Banksy - The Unauthorized Exibit at Sotheby's. My son, the art student, turned us on to his work.
Wikipedia succinctly describes Banksy's work, "His satirical street art and subversive epigrams combine dark humour with graffiti executed in a distinct stenciling technique. His works of political and social commentary have been featured on streets, walls, and bridges of cities throughout the world."
Freedom of Thought
Freedom of Expression