The notion regarding ownership of a guitar may have been helped along
by Albert Bigelow Paine when "The Boys Life of Mark Twain" was
serialized in _St. Nicholas Magazine_.  The January 1916 issue
features an illustration by E. F. Ward showing Sam playing a
guitar.  The question arises whether or not Paine approved the
illustrations for _St. Nicholas_ or whether or not the illustrator
used his own imagination.  Paine writes when Sam was living in
Keokuk he joined a music class but "He was never a great musician."
While Paine never specified the instrument, the illustrator did.