There are a variety of ways you can get hidden messages into ordinary messages.
Acrostic poems are the most common example of this – where the first letter of each line creates a word.
In cosykiller we use a few different hidden methods of communicating. Acrostics, and also underlining or marking of text in other ways. We even use missing letters as a puzzle. (That’s a big hint.)
Some codes are hidden in plain sight – like morse code in a border graphic, or braille (which is also a letter substitution code). Sometimes you need access to two or more sheets to read a message which is split between two or three pieces of paper. Or you need to fold the paper in a certain way to reveal the message.
As well as plain sight hiding of messages we also go in for hidden messages by way of steganography. (You might know it as a lemon juice secret messages).
Back in the olden days, the only way to read these was by heating up the paper. In modern times (to save you all burning various bits of the game by accident) it is possible to reveal lemon juice ciphers with UV light.
Other ways of hiding messages are in different coloured overlays. these work in a simliar way to the simple colour blindness tests you’ve seen where those who are red/green colour blind see a totally different number to everyone else.
There are also ways to multi-part a cipher – by splitting the code over several sheets. Using tracing paper overlays on specific text to reveal a message (or a design).