Re: Cipher books mixed with art, thoughts.
I can think of only 2 things vaguely like that, that I'm aware of, and that other people are generally aware of. Tolkien's runic script, and Klingon. Both are aspects of a fantasy world building exercise. In Tolkien's case he was a linguist. Apparently all of Middle Earth exists to support and explain the imaginary language he was creating! No reason for anyone to speak in any particular way if the world doesn't have a history, with people moving around and diffusing their concepts. So would be the linguist's take on things I imagine.
The important thing to note here, is whether you're enjoying reveling in obscurity and mystery, or whether you seek to explain something by making a language. I think the reason I actually know about Elvish scripts and Klingon, is because the authors were trying to communicate with me about the worlds they were describing. Klingon isn't a mystery, it's a reality. It's a contract with the audience, that the author seeks to explain something.
I don't think most people know about ciphers and deliberate obfuscations, because there's nothing for the audience to hang their hat on. The packaged goods are "mystery". When mysteries aren't explained, they are all the same. How would anyone ever know one work from another? Random scrawlings that can't be translated, don't mean anything.
In human history, the written scrawlings have often been accompanied by images, or are images themselves, i.e. Egyptian hieroglyphics. In the case of pictoral human languages, they were attempting to explain things, we just didn't know what they meant. We could make some guesses based on the pictures. The subject matter could be abstruse if it was religious, as who knows what kinds of cockamany beliefs people had. But many scenes were practical, such as kings killing adversaries, raising crops, being entombed. From these we have a basis for figuring things out.
Ultimately though, the game of historical decryption is to find a Rosetta Stone.