This is a well-written, interesting book and I'm not sure why it was made.
Red Sign is an oddity, a crossover book in a game line that usually paid lip service to crossovers while not really doing anything to encourage them. It's about multiple conspiracies of vampires and mages who are searching for a way to transform a vampire back into a mortal, the fabled "Ritual of the Red Sign." To that end, there are members of both groups chasing down rumors of ancient tomes, reaching out to potential allies in the conspiracy, researching forbidden knowledge, cooperating across sect and supernatural grouping lines, and otherwise forming a cabal with the goal of, as one Vampire sourcebook put it, rolling more successes than G-d.
This sounds amazing, and the book does a good job of providing ways to tie other characters into the search for the ritual. Maybe they're Sabbat templars, out to squash this ridiculous idea of turning superior Cainites back into juicebags. Maybe they're Progenitors who are intrigued at the idea of curing the "disease" that is vampirism and the obvious utility of a ritual that can resurrect the dead. Maybe after their time in the Lair of the Hidden, they've determined that Golconda is a fool's errand and the only hope of redemption is becoming mortal once more. Maybe they're members of the Order of Hermes who want to heal the Massassa War by bringing the Tremere back to life, or they're Tremere who hope to turn undead vampires back into living wizards to provide an edge when the Antediluvians awaken. There are plenty of possibilities for any number of groups to get involved.
There are also rules for ancient tomes of secret lore that allow mages who possess them to perform otherwise impossible feats of magic, magic that might be difficulty 11 or even higher, or normally have Sphere requirements beyond the mage's capabilities but are lowered when using a tome. I've heard several complaints before about how the structure of Mage: the Ascension, with the way that paradigm dictates magical expression, means that seeking out ancient and forbidden tomes is basically pointless because all foci are merely tools that are discarded as mages grow closer to understanding the nature of reality. The tome rules sidestep that, but to the benefit of the game, I think.
But it's a lot like Lair of the Hidden in that it's an extremely specific scenario that creates a long-term change to the world if successful. In Lair of the Hidden, success results in a dozen vampire Methuselahs, masters of blood sorcery and ancient knowledge, let loose upon the world. In Red Sign, it returns a vampire back to life. Maybe the ritual works extremely well and creates the Redeemed, a being that has passed through dead and returned and bears a portion of eternity within their restored soul. Maybe the ritual went awry and the former vampire is a soulless monster, its Beast integrated with his mortal personality. But either way, the former vampire is a walking Masquerade breach, a mortal with all the knowledge of their vampire existence, that must be dealt with. And if the ritual can be done once, it can probably be done again. Even if the ritual is only performed by NPCs, if it works, then it's possible. And if it's possible, what else is possible? Can people use the Ritual of the Red Sign on their enemies, making a vampire human and so removing a rival? Can it be used at a distance? Will a group of failed monsters help the Nephandus conspirator in his goal to unmake the world? These are all high-level questions.
And that's why I only rated it three stars. The crossover, the world-changing, the Redeemed, all of that is very high-level play that most Vampire games are never going to reach. It's possible to run Red Sign as an investigative chronicle, chasing down rumors of books and cultists, almost more like a Call of Cthulhu game, but that ignores a lot of the material actually presented in the book. Most of it is only useful for an extremely specific kind of game and the other kind of games that would use it would only use a small part of it. For those people it's great, and for everyone else, well. There are other books.
One of the Vampire books that came out after I had lost interest during the Revised era. I had heard a lot of bad things about it, but after finally having read it, it's not so bad. It's just that it could have been so much better. I guess what I really dislike is how much effort the authors put into justifying how incredibly "different" their approach to the subject matter supposedly is and how they break with established canon by reintroducing concepts and events that had been there right from the beginning before being ignored and disregarded by later authors, while simultaneously looking down on longtime players/readers. Still, not too bad a book.