Maybe you do not work for the government services and you are not a professional spy or intelligence officer. But you use secret codes every day. They surround you everywhere. They are in your wallet too. There are known symbols that urge people to stop: in most countries it is red, but there are also countries where it is the opposite. In China, this color is associated with the holidays. But such signs cannot be secret, they should be clear to anyone. There are other letters — they must be understood only by certain people. Foreign languages are also a cipher for those who do not know them. There are such codes that are understandable only for small groups of people: certain words, pictures. Even clothes can be familiar — it shows the mood you are in right now.
