The Grime Writer is a chunky marker pen that gets filled with soapy water (or other cleaning solution) and is used to tag dirty surfaces. It is available to purchase online at either Suck UK (link) or Cool Material (link).
…Use it to tag your dirty vehicles & windows, or to transform dirt into artistic expression.
Much more socially acceptable than real graffiti and (more importantly) a lot less illegal – Grime Writer helps you leave your mark wherever you find muck. Use responsibly to help promote the phenomenon of negative graffiti, and brilliantly combine the crime of defacing a bridge with the community service time cleaning it up again afterwards, into one harmless, helpful, creative act.
images via Suck UK