Please refrain from willingly picking the naive interpretation when you've understood my point perfectly fine, it's against the rules of this website.
...sigh:
Secret codes as in "watermark-level omission of characters" are a myth. Lingo and jargon do however exist, and convey meaning in a particularly subtle way. They are shared and taught by culture, not by a secret handbook passed down from generation to generation. See also dogwhistling.
The goal is to protect the issuer, not to selflessly inform the recipient.