Kurt Cobain's Martin D-18 is found at the Martin Factory in Nazareth, PA. The plaque located under the guitar reads, "This well-worn D-18 was coined 'Grandpa' by Cobain himself, and was gifted to the rocker by then girlfriend Mary Lou Lord in 1991. The guitar was was used by Cobain by while on tour for Nirvana's second and most notable album, 'Nevermind'. Here's a pic of the guitar as well.

In this photo, John Frusciante can be seen playing a Martin D-18 (it is not a D-28 as there is no white binding around the body). This same guitar can be seen in John Frusciante's bedroom on the documentary "Funky Monks", filmed during the recording of "Blood Sugar Sex Magik" (see at 57:05 on this link : https://www.youtube.com/watch?v=4Z3Gnbgjq0M). This Martin D-18 is therefore possibly the instrument used during the recording of the song "I Could Have Lied". It is possible to notice that the bridge pin of the G string on this guitar is white while the others are black ; this bridge pin was certainly swapped with one of the bridge pin of the 12-strings guitar used by John Frusciante during the recording of the song "Breaking The Girl" (this 12-strings guitar has 11 white bridge pins and 1 black bridge pin as you can see in the photo of this link : https://www.groundguitar.com/john-frusciante-gear/john-frusciantes-12-string-acoustic-breaking-the-girl).

David Gilmour used a Martin D-18 from 1945 during the 2015 "Rattle That Lock" sessions, as confirmed by Bjorn on Gilmourish.

Used for this live performance with Myles Kennedy

In Episode 4 of "Guitar Moves" on YouTube, Dan Auerbach of The Black Keys is seen playing a Martin D-18. Auerbach's 1960 D-18 was later put for sale at Gruhn Guitars, as a part of "Dan Auerbach Collection".

Brian acquired his first D18 in the early 70s and recorded “Funny How Love” on one.

"His main acoustics are a Martin D-45 that he got in 1967, a prewar D-18 and a D-28. I've installed stereo Fraps in each, which is by far the best way to amplify an acoustic guitar. I place two pickups inside the guitar-one for the top three strings and one for the bottom three. I do it real time while stringing up the top three strings . I have the pickup hot through a nice P.A. system,and I move it around."

"I had the amazingly good fortune to meet another incredibly talented songwriter named Elliott Smith. He set a new bar for music and I truly believe him to be one of the great voices of our generation. In 1995 I took Elliott out on his first tour as my opening act. I adored his songs and our friendship ran deep. Although our relationship was strictly platonic, it was Elliott who helped me fill the void after the loss of Kurt. On both of the tours that Elliott and I subsequently did together, it was the Martin that we would end up playing into the wee hours of the morning in our hotel room…I believe that "Grandpa" is the ONLY instrument in the world that was played, adored and loved by both Kurt Cobain AND Elliott Smith. It was also played on occasion by Shawn Colvin and of course, me. In 2003, Elliott died and this completely broke my heart…It was around this time that I began to release myself from the whole world of music as I knew it and dedicate myself to my young daughter Annabelle. The Martin was getting little attention, and by this point it held memories that I wanted to let go of. It had served me well and I wanted to give it a new lease on life. It needed to be played, so in 2004 I sold it to a guitar dealer and that was that. A few years later I got a letter from someone who was about to purchase the guitar and wanted to know if everything was on the “up and up.” I am happy to say that the guitar Kurt Cobain called “Grandpa” and Elliott Smith called “Gramps” now resides in the permanent collection of Make’n Music in Chicago, IL. I am told it is played regularly and adored by many a visitor who wants to hear the “stories.” On special occasions it is even made available to other musicians for purposes of inspiration and to use on recordings. I am glad to have known it, served it well, and to have shared in the memories this wonderful guitar possesses. There you go…the story of “Grandpa.” Mary Lou Lord

Jerry Garcia used a Martin D-18 acoustic guitar during the recording sessions for "Workingman's Dead" and "American Beauty," as detailed in the guitar history on Dozin.

Freddie recorded "Crazy Little Thing Called Love" with an extra mic on a Martin d18.

In an Instagram post by Mark Morton, he displays a Martin D-18 from 1948, captioning it as one of his "old cuttin’ boards."

Elvis Presley is associated with a Martin D-18 acoustic guitar, as detailed on Scottymoore.net, which discusses his second D-18.