I have that LP recording, although not autographed. It has nothing to do with the author Samuel Clemens, although the song is from 19th-century riverboat culture. "Mark twain" is elliptic slang for "marking on the twine" used to measure the depth of the river. Harry Belafonte sings beautifully, but if any Clemens collector wants it for any reason other than the singer's voice, I'd be fascinated to know why. Vicki Richman Bedford, Brooklyn NY