Kathryn has replied to my earlier post (Can anyone read shorthand?) with a translation - which is not very secret - but reminds us that many people exchanged post cards merely to add to each other's collections. (Perhaps a bit like the way some people now collect friends on Facebook!)
Dear Mr Uphill Thank you for your lovely postcard of Dorchester. You said I think that you liked pictures of churches. Have you ever seen a photo of this church before? I myself think that houses would be such a delightful collection of postcards. You said that you like foreign correspondents best, I think everywhere today, I have a correspondent in China, Malta, Gibraltar and in America, and find it very interesting indeed. Yours sincerely
So my Hidden Messages page now has two examples - but I would love to find some more on Hertfordshire cards. Definitely some used number codes (1=A, etc - or even more sophistcated).