Reverse Graffiti

From Wikipedia:

Reverse graffiti also known as clean tagging, dust tagging or grime writing, is a method of creating graffiti on walls or other surfaces by removing dirt from a surface. It is usually done by removing dirt/dust with the fingertip(s) from windows or other dirty surfaces. Reverse graffiti on windows/glass can be highly visible due to the reflection of sunlight.

"The skulls belong all to us. I wanted to bring a catacomb from the near future to the present, to show people that the tragedy of pollution is happening right now. I try to remind people of things they are trying to forget." - Alexandre Orion.