Grime writer is an ingenious marker pen that gets filled with soapy water and is used to tag dirty surface.
Here's what the creators of the Grime writer had to say.
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.
The down side to the grime writer, no as much fun to sniff.