Apologies for delay, but thanks for suggestions. Have watched some episodes of "Porridge" to see if Ronnie Barker received messages in a pen, but no luck so far!
Bonnie Parker was half of Bonnie & Clyde, but I don't recall she sent messages to Clyde in a pen. Reckon I'll settle for Ronnie Barker.
Thanks very much for help. Hope you had a good Christmas and all the best for new year!