Jargon Watch: Negative graffiti | 行话 负涂鸦

Grim from pollution to tyre and shoe rubber build up grim on roads, pavements and buildings and street cleaning doesn’t go sufficiently deep to remove it. However, with a stencil and a powerwash it can also be the canvas for art or corporate graffiti.
Negative grafitti
I found this example for a London-based business IT company at the top of Neal Street in Covent Garden.