This is an old revision of the document!
Blackletter is the font of the stylized letter “S” found on the Cover Sleeve (Slipcase) as well as the S. (Inscribed Image) on page xiii. This particular font was used from around the 11th century in Western Europe. It is also worth noting that there are ties between this particular font and traces of Nazism.
According to an article by Bleeding Cool, this fonts use used in one of the first teaser trailers released for S. allowed for connections to be made back to the book. This article can be read here.