Grime Writer: detergent-filled graffiti pen

Grime Writer is a detergent-filled graffiti marker that cleans away
street-filth to leave your message behind. There's a good chance that
the graffiti you create with these is no more legal than any other kind
-- there've been successful prosecutions against companies in the UK
that paid "street teams" to "reverse-graffiti" their messages by using
detergent and stencils to selectively