That sketch was made for a postera* advertising Mark Twain's lecture
at the Brooklyn Academy of Music, February 7th, 1873.**


* Mark Twain Himself by Milton Meltzer, p.118
**Mark Twain Speaking by Paul Fatout, p. 650

The illustration itself is in the New York Public Library.

Hope this helps.
Richard Henzel
www.richardhenzel.com/marktwain.html