Now, they claim this is "ancient"... I don't think so. I think this has been created because of the runes, ogham and the Hebrew letters in tarot cards - these "symbols" look sufficiently mystical and if you can sell it, do so.
Now, there are at least two different methods. One uses the letters as runes, the other uses dice or sheep knucklebones to come up with the symbol.
Apollonius Sophistes' method with dice
The tile method