Banksy describes in wall and piece that it happends (maybe more than once) that he got interrupted while spraying (nice anecdote if you have the book, one of the first stories in there). So the missing Y wont be a problem in that case..
where did you find the picture, or did you make it yourself? kind of curious.. as this would be still riding it would have been there for at least 10 years...
[br]FS: 2 x Martin Whatson OG. 2 x Adam Smithmada OG. PM for pictures.