The typewriter that belonged to H. L. Mencken. Photo by the Enoch Pratt Free Library, Baltimore, Maryland. [Update, April 15, 2007: The photo has moved, and is restricted by copyright; you may follow the links to view the original photo of the typewriter, at the site of the Enoch Pratt Free Library. E.D.]
Was this the machine upon which Mencken composed the Millard Fillmore/Bathtub hoax? Perhaps. It was used prior to 1930.