Not all codes are designed to be written and sent (either digitally or physically), there are also spoken codes. The most famous spoken code is probably the Navajo code talkers in world war II.
Pig Latin is a really simple code, but when spoken fast, it’s a good way of stopping people snooping in on your conversations! There are apparently variations on pig latin, but below I have put as much detail as I can find.
Words which begin with a single consonant take all the consonants that appear before the first vowel, and add it to the end of the word. Then add ‘ay’ after the consonant.
For Example: fish = ishfay shark = arkshay
If a word starts in a vowel, you simply add ‘yay’ on the end.
image = imageyay ian = ianyay
Navajo Code Talkers
Take a look at the text on wikipedia for more information on this. The real advantage of this code is that someone didn’t have to sit down with special code equipment, such as a code book, or a crypto machine. This meant that fast and secure communications could be sent, both of which are vital parts to battlefield comms.