Our correspondent, BOAC, set me off on a Google search for his image. Hitherto, alas, to no avail, but there are still 150 pages to view...
En-route, however, I was diverted to one of many contrail websites. This one:
Appleman Chart - Student
takes you to one claiming that the United States Air Force produced contrail prediction charts. It says: "Background: Military planners have been interested in condensation trail (contrail) forecasts since World War II. Contrails can make any aircraft easy to locate by enemy forces, and no amount of modern stealth technology can hide an aircraft if it leaves a persistent contrail in its wake. In 1953, a scientist named H. Appleman published a chart that can be used to determine when a jet airplane would or would not produce a contrail. For many years, the US Air Force Global Weather Center used a similar chart to make contrail forecasts."
The page illustrates such charts and gets you to compile your very own contrail forecast. There's also a student version!!
Now, BOAC, your image must be out there somewhere...
See you further down the logbook!
DIFAR