Adding MD to your name gives the readers a belief that you are qualified to write on a subject. I seldom use Ph.D. after my name but I have on occasion used CPL AUS DIS as a gag, the meaning being Corporal, Army of the United States (e.g. draftee) Discharged. I have a friend who had two Orders of the British Empire (OBE) but never adds them to her signature.
I would never use Ph.D. after my name, and I would never read a book by someone who has to bolster his credibility that way. For that matter, if this book is a mystery, how does the M.D. lend any qualifications?
I should add that the addition of degrees also disqualifies non-fiction since it generally signals that the book is an unscientific attempt to sell to the masses. In non-fiction you look at the publisher's blurb, and at the bibliography and the index in the back to make sure the author is qualified to discuss the topic.
If you are writing a medical mystery or a book that requjires the author be qualified to write on the subject, the academic degree is appropriate. One sci-fi author was E.E. Smith, Ph.D. If an author is writing about Christianity, for example, would you question the authenticity if the author identified himself as a rabbi? Mormon?
It all depends if the book is written for the general public or for the research community. I don't buy non-fiction that isn't research. I don't need the author's titles, because I take those for granted. What I look for are those other markers that show the book to be serious-research-based.
Would a rabbi write a book about Christianity? My guess is if he did, the publisher would announce this in the blurbs. Is think any popular books written by Ph.D.s and M.D.s should be similarly introduced if it's relevant.
Besides, let's face it, a lot of those degrees are of dubious origin.
Not all non-fiction has extensive bibliographies, notes, and indices. These are necessary to readers who want to further their understanding of the subject. They also tend to be vetted by other authorities in the field. In other words, there are various levels of reliability and effort involved.
I stopped by for a chat with Kate Shugak. THE SINGING OF THE DEAD and A FINE AND BITTER SNOW. Word is Dana Stabenow finally found someone willing to film the series in Alaska, so she has sold the movie rights. How anything could equal the books I don't know, but I won't miss watching them.
Watched "Frank Herbert's Children of Dune," so now I'm reading the books it was made from.
Just finished the winner of the Inaugural Text Prize for Young Adult and Children's Writing (unpublished manuscript) - The Billionaire's Curse by Richard Newsome. Billed as Indiana Jones meets the Famous Five, it had a rather quaint, sort of good old fashioned kids story feel to it - reminded me very much of the sorts of books that got me hooked as a kid. Last night I started Stone's Fall by Iain Pears which is a thumping big 596 page doorstopper of a thing!