The best secret “font” or code to all non-Germans (or even to Germans below a certain age) would probably be old German ‘Suetterlin’ handwriting font.
[ Karin says : ] I’ve just watched the beginning of the film “The White Ribbon” on BBC iplayer. I always tend to watch with the subtitles turned on. The opening credits began, and the words “Das Weisse Band” appeared, which were then translated by the subtitles correctly as “The White Ribbon”. But then, underneath the main title, slowly a writing appeared, as if being written by hand. It was written in an old German handwriting font / script, the one which is called ‘ Suetterlin font ‘ or Kurrent , which had been used in Germany as the primary script in variations between 1915 and 1941. I myself went to school from 1970 to 1983, so it was never my primary script, but as a pupil I found it listed in a few books alongside other examples of scripts / handwriting fonts, and I taught it myself to be able to read my father’s old exercise books.
Anyway, the writing, that was slowly revealed among the opening credits, read “Eine deutsche Kindergeschichte”. It was never translated in the subtitles. And then it occurred to me that the subtitles’ writers probably never were able to read it. (It means “A German children’s story”).
So, if you are looking for a secret script / font / code to all non-Germans and even to all Germans below a certain age, you don’t need to look any further than Suetterlin / Kurrent scripts / handwriting fonts.