I would agree with Jason that the term mechanic's grip was indeed coined by Mickey MacDougall; however, the term was not used in the Cosmopolitan article.
The first use of the term was in an AP article in the Trenton Evening Times (Trenton NJ) dated March 27, 1938. The headline is, "Woman with Shiny Nose May Be Gambling Cheat, Declares Card Sleuth, Exposing Racket".
In the article, MacDougall writes, "There's one best way to spot a cheat. Beware if you see a player holding the deck with his index finger backing up one end of the pack, three fingers curled on the side, and the thumb held diagonally across the top. That's the mechanic's grip, the only grip that permits the bottom deal, the second deal and the top deal with the same hold."