The couple saw brushes and paint cans in front of a paint-splattered canvas at a gallery in a Seoul shopping mall. So they added a few brush strokes, assuming it was a participatory mural. Not quite : The painting was a finished work by an American artist known for his abstract aesthetic riffs on street art. "Graffitied graffiti," a local newspaper headline said last week about the piece by John Andrew Perello, the graffiti artist known as JonOne. The artwork is displayed with paint cans, brushes and shoes that the artist used when he worked on it, one of the exhibition's organizers, Kang Wook, said in an interview. He added, "There were guidelines and a notice, but the couple did not pay attention." Others say the sign was confusing and the couple should not be blamed. And some say the couple's abstract brush strokes — three dark-green blotches (in the center of the painting, above) — improved the piece. The artist said he was disappointed and angry that his work had been "defaced," although some people have said the publicity could work in his favor. He said the incident reminded him of growing up in New York City and the feeling that his talent was not appreciated.