Don't want to veer too much from stocks, but this letter I just found from an affectionate incarcerated Al Capone to his young son is pretty amazing. It recently sold for $62,000.
"Well Son, here is your dear Dad, with a letter for you, and pray to God, it will find you, in perfect health…Junior keep up the way you are doing, and don’t let nothing get you down. When you get the blues, Sonny, put on one of the records with songs I wrote you about to Ma, to you, which I sure go to town playing them... [much more]"
Here Scarface brags about his musical talent to his young son and describes his days in "The Yard"...
Bizarre: Capone recommends that his son subscribes to "Fortune Magazine"