The sight of a paddle steamer is synonymous with Mark Twain. Thomas Kelley/iStock via Getty ImagesAfter trying out other aliases like “Thomas Jefferson Snodgrass” and “Sergeant Fathom,” Samuel Langhorne Clemens adopted “Mark Twain” in 1863. Samuel Clemens's signature was discovered in the Mark Twain Cave in July 2019. The Mark Twain National Forest could’ve been named after a different famous Missourian. A photo of a lookout tower constructed in Mark Twain National Forest.