Roy's last post woke a long-dormant brain cell. It led me to an album where I found a copy of the cover he showed. Next to it was this card, created around the same time and also signed by Arnold Machin.
There are 500 copies of this one, and the back says that proceeds will go to a charity of Machin's choice. These cards show up on eBay from time to time.
While we're on the subject of Machin autographs, I have one other. It's a page in a Machin album that was sold in the 1970s and 1980s by Urch, Harris, a British stamp company. If anyone has any more information, such as the beginning and end dates of sale of the autographed album, let us know.
I used it for a few years, then gave it up for two reasons. First, they replaced whole pages every year in order to add just a stamp or two, and I got tired of remounting. Second, I became interested in varieties for which there were no spaces in the album. So I decided to stop getting updates, but I kept the album because of the autograph.
If I recall correctly, Urch, Harris was bought by Stanley Gibbons.