The Daily Genealogy Transcriber is a site owned by my friend, Michael John Neill, where every day a new handwriting sample is posted. The sample is usually a signature. Readers can guess at the interpretation. Michael says that he usually knows the answer. He waits at least 24 hours before posting the answer.
All submissions have to be approved to cut down on spam, but all guesses are usually posted.
Old images, with guesses and answers, are left up which makes for interesting reading. Seeing how others read a name gives additional insight into indexers and indexing errors.