This is one of those easy to create products that you create once and just let it make money for you day in day out.
Nothing fancy, just create a simple ebook on how to interpret handwriting, put up a simple sales letter and sign up for a Paydotcom.com or Clickbank.com account.
You can find all the content you could ever want about this subject athttp://www.myhandwriting.com/FAQ/
and
http://web.singnet.com.sg/~tjlow/graphology/ grapho.htm