From the White Wolf Wiki, the most complete White Wolf reference

Hunter Code is a language made by the Messengers so that the Imbued can communicate with each other. Only Hunters can understand it or, in many cases, even notice it at all. It is often merely overlooked by any supernatural creature. Each symbol usually has a one-word meaning attached, and some symbols are harder to understand. For example, an Avenger would have a hard time understanding the meaning behind the symbol for "Friendly monster", because they're not inclined to see a monster as anything other than a target). The only Hunters capable of creating complex symbols are the Visionaries, as it is their Creed Ability.