"I am a naturally peaceful person, but I wouldn't be that upset if 'Vladimir' accidentally met with a baseball bat," - an art lover @twitter — The Guardian
The Guardian reported "A man has defaced a multimillion-pound Mark Rothko mural hanging in the Tate Modern gallery in front of onlookers. A police investigation is now under way into the vandalism of the US artist's work.
The graffiti on the painting appears to read "a potential piece of yellowism." According to an online manifesto, Yellowism is an artistic movement run by two people named Vladimir Umanets and Marcin Lodyga."
A related discussion on graffiti and tagging on Archinect "Graffiti Culture Thesis"