You've made a mistake here. Lots of the people's letters you've used are practising artists and can easily take legal action against you for using their artwork, including myself. I know most of the people here that you've used and I'll be informing them that this has happened. Not all graffiti writers are incapable of taking legal action with these things for fear of getting in trouble themselves as they have already been charged therefore can openly claim this artwork. This is where you are going to find problems.