Handwritten note with sketch, Keith Haring.

This little drawing was found folded up inside a paperback book that I bought from a flea market in south wales last year. It appears to be drawn by the American pop artist Keith Haring. As to it's authenticity ? I am not an expert and have no idea whatsoever. The paper is very thin and there is a number 40 printed on what I presume was originally the bottom of the sheet, it looks like it has been torn from a bar / restaurant notepad. It did have some creases where it had been folded, I have recently pressed it with a hot iron (after placing it between 2 sheets of clean paper) and the creases are now barely visible. The size is a modest 4" x 5 3/4".
I will be leaving the UK on Thursday evening and will be returning on Tuesday 2nd, I will post upon my return on Tuesday / Wednesday. Sorry, but I will not be able to respond to any questions while I am away, but feel that there are no further details I could give anyway.