There has been no standard bibliographic identifier for English Jules Verne books. In fact, it is only fairly recently that there have been English Bibliographies!
The second comprehensive bibliography in English (following the excellent work in the "Jules Verne: a primary and secondary bibliography" by Gallagher) was titled ..... and was written by Ed Meyer, a book dealer who ran Country Lane Books.
This page will show a "Meyers" bibliographic identifier in the form of Mxxx where xxx is the page number in the Meyers bibliography.

The best English bibliography at the moment is the Jules Verne Encyclopedia by Brian Taves and Steve Michaluk jr. In this book, the authors have attempted to identify EVERY English edition of All Verne's titles!
Since it is the most complete bibliography to date, many sellers and collectors have adopted their numbering scheme when referring to Jules Verne's books in English. The identifier takes the form of Vxxx where xxx is the id number that Taves/Michaluk assigned to each Verne title. Note that only 1 identifier code is assigned for each title, even though the sections in the Encyclopedia dealing with each book lists 10, 20, 30 or more books.

 This page will cross reference English and French titles of Jules Vernes works along with the various bibliographic identifiers (Margot French bibliographic identifier, Meyers bibliographic identifier and Taves/Michaluk reference number)