John Mayer’s Martin 000-14 Cutaway Custom
This Martin was mostly used just for the 2001 Room for Squares tour, it being one of only two Martins that John was seen playing around that time (the DM3MD being the other one). It was likely picked up just due to fact that it was a cutaway guitar, and allowed John to reach the higher frets more easily while playing live.
Unfortunately, trying to figure out the exact model of the guitar proved fruitless. It seems to feature a cutaway body with OM/000-14 design, and Abalone binding on the edges and around the sound-hole, but surprisingly – no binding on the neck whatsoever. This is weird because the Abalone binding seems to only be available on the top of the line models (Martin 000-42 for instance), and it appears that these models all come with neck binding of some sort at least. Also, these models usually feature custom fretboard inlays as well, while John’s guitar seems to have the basic dots.
This could all point towards a custom-made guitar, or maybe a Signature model that has since gone out of production. As always, f you happen to know something that would help identify the model, please be sure to shot a message.