I found this while I was researching the tap code. In addition to the tap code the advice to potential prisoners had another form of manual alphabet.
Disclaimer: “As an Amazon Associate I may earn from qualifying purchases.” Adsense and Infolinks were no help at all.
If you have enjoyed this article or it has been helpful to you please feel free to show your appreciation. Thank you.
Read The Third Wave by Alvin Toffler!