trying to remember a book

a while ago i came across a mention on this sub about some older cult's book full of symbols and codes that no one has ever been able to decipher. it's supposedly a little infamous and i remember wanting to read it so bad but now i cant for the life of me remember what it was called. the description i gave probably doesnt narrow it down very much but if you know of literally any book that fits it at all please please let me know