The Glyphosphere is a mysterious source of communicated information. Information about Allison having a Key of Kings was all over the Glyphosphere. When inside of Throne, one is able to speak anything they like into the air and make it into glowing glyphs (if they speak through the right device). It is then possible to retrieve messages and transcribe them if needed.
It is like a magical internet (as implied by the comic). If one registers with a guild that answers to Mammon, then written information can be magically communicated between surfaces that can be written on (individuals may use a book or a similar object of their choosing). Mammon created it. One speaks glyphs into the air, the message turns into bird, and it arrives as a letter to the intended recipients.