Ciphers are a secret or disguised way of writing. Ciphers and codes have been around a very long time and have seen endless variations and iterations in order to confuse those who aren't meant to read its contents. In recent times we use computers to come up with complex algorithms in order to encode our private transmissions, however I am partial to the old-school, analog method of encoding. This paper postcard decoder
is a very basic, entry-level approach to understanding ciphers and is great fun for postcards.
This postcard decoder
is placed over your postcard and can be used to encode a message, then decode the message after it's been sent. The cipher code can be sent either in a separate transmission or hidden somewhere on the package itself, allowing savvy codebreakers a clue on how to decipher your message. Though this cipher is not as sophisticated as some digital ones, it's a fun, low-tech and effective!
Here's what I used to make my postcard decoder:
pencil and rule (or computer printer)