Update: William Newman has the true history of this artifact: "May I confess to being the perpetrator of said 'board', which I drew on a sheet of paper back in the 1950s when I was in my early teens and lacked the money to buy a proper set. My brother and I played on it, and when Alan asked if he could join us in a game we played a threesome (Alan lost). Later the board fell into disuse and I lost track of it about 50 years ago, but it recently turned up (together with the rules), see http://www.bletchleypark.org.uk/news/docview.rhtm/644565. The Roman numerals indicated property prices. I forget why I added the diagonal. "
Yesterday, I had the delightful experience of attending a fundraiser for Bletchley Park, the birthplace of modern computing and cryptography, where the Allied WWII cipher-breaking effort was headquartered. Cold War paranoia caused Churchill to order Bletchley broken up, its work kept secret, its machines destroyed, and, very slowly, it is being rebuilt.
Earlier this year, the Bletchley Trust acquired Alan Turing's papers for the collection with a grant from Google.org, and I got this shot of Turing's awesome hand-drawn Monopoly board -- the cryptographers of Bletchley were sequestered from the rest of the world and desperate for distraction, hence this great bit of historical ephemera.
I also learned that Turing didn't believe the UK economy would survive WWII even if the Allies won the war, and so he drew as much of his pay as he could in silver half-crowns, melted them down, created two enormous ingots, and buried them somewhere in the region. They've never been recovered -- as far as we know. (finkployd just reminded me that this was in Cryptonomicon, but the detail had slipped my mind).