I first happened across a version of the song on an LP by Sally Rogers (In the Circle of the Sun). She mentions that a short snippet the Prisoner's Song is played at the end of a Humphrey Bogart movie "Deadend".
I was once watching a Buster Keaton silent film on television. In the story he at one point is put in gaol, and I was surprised to see the words of the Prisoner's Song on a piece of paper posted on the cell wall. The shot was of Keaton reading the sheet, and it was definitely the same song, although I only saw it briefly. Unfortunately, I cannot work out which film the scene appeared in to be able to set a date for the words being in print.
I just thought I would add the information just for the sake of completeness.
Quack!
Geoff the Duck.