Concrete and Clay

I was in Tate Modern a few weeks ago killing time and looking again at the Rachel Whiteread installation when I stumbled across a small white box with a message inside:

"Thank you for taking time to investigate one of an edition of 'more white boxes'. Once you read this message please acknowledge your find by emailing morewhiteboxes@googlemail.com and leave your details where you found your box."

I picked up the box, put it carefully into my bag and went into the bookshop, where (ironically) I was looking for an edition of Banksy's existencilism. Once I got home I emailed my details and started a correspondence with the artist; her next move is to place her own postcards of the Whiteread installation into the Tate bookshop amongst the originals. It left me thinking - how would you like to leave your mark?