M-Type flavoring is really Tabanon (aka Tabanone).
According to an internal memo from British American Tobacco dated 7-21-89 (yeah, this stuff is all out there....and I'm sifting through it all!):
"Tabanon is a mixture of five components...
They have been identified to be tobacco constituents and are nature identic."
Another document describes Tabanon as having a "strong Oriental character," which in cigarette talk means it tastes a lot like Turkish tobacco. It was originally primarily used as flavoring for cigarettes in countries that had banned the import of Turkish tobacco, and was not considered economically feasible for the U.S. because it was actually more expensive than Turkish tobacco.
I love the stuff...I actually think my favorite synthetic tobacco juice, Hangsen Desert Ship, is nothing more than a light dose of Tabanon and an even lighter dose of diluted Tobacco Absolute.