Some believe "Mark Twain" was a reference to a leadsman's call. The leadsman's job was to toss a weighted line overboard to measure the depth of the water. On a Mississippi steamboat, he would do this again and again, calling out the results to the pilot. The depth was measured in ''fathoms,'' where a fathom is six feet. "Twain" is an old-fashioned word for "second." "Mark" meant the depth was on the exact fathom mark, much like describing a time as "on the dot." So "mark twain" literally means "two fathoms."
Others believe that "Mark Twain" refers to a then -common method of ordering whiskey. "Mark Twain" referred to a double shot of the cheapest whiskey in the bar. Twain's penchant for cheap whiskey and cheap cigars lends credence to this theory.
In ''Life on the Mississippi,'' Twain says that he worked for a captain who used to send "brief paragraphs of plain practical information about the river" to the New Orleans Picayune (the famous newspaper), signed "Mark Twain." According to Twain, this captain always added little reminiscences about things like islands that "disappeared in 1807, if I remember rightly," which were annoying and drew the scorn of other captains. Twain wrote a humorous parody, without thinking about the captain's feelings, and was printed in a newspaper: