reverse graffiti

(名詞) 反向塗鴉 - 巧妙地清除某個表面或牆面上的塵垢、污垢或污漬所形成的圖案或文字塗鴉。

Pollution residue on a stop sign. Algae at the bottom of a public fountain. For most people, such accumulated grit is a dirty, if often overlooked, fact of modern life. But for "reverse graffiti" artists, that dirt is a beckoning canvas. —"Reverse Graffiti," O, The Oprah Magazine, February 1, 2012

Also in the show are the American artist Jim Dingilian's smoke landscapes in a bottle, which have the elusive look of memories, and the Brazilian artist Alexandre Orion's video of his "reverse" graffiti, carved into the soot-saturated walls of São Paolo traffic tunnels.
—Alix Browne, "The Other Ash Can School," The New York Times, February 7, 2012