This page contains spoilers about the Heartbound ARG. If you want to solve the puzzle yourself, avoid reading this article.
Currently, very little is known about Guardian Glyphs. Binder and Lore have both been seen casting spells while "speaking" in them, while the villagers of Animus have been seen writing in them on Heartbound merchandise, as has the author of the pages in The Spine, that presumably being Binder.
If you enter the following code at the title screen of the game, you'll hear a faint laughter, and the in-game guardian glyphs will be translated for you:
This code was discovered through the ARG.
Cirsi Shirt: "SULFUR MERCURY SALT"
Emelio Shirt: "HERO"
Ramul Shirt: "RAMUL"
Remé Shirt: "ITS A SECRET"