The glyphs illustrate an emissary of the Qiraji meeting with three silithid at the bones of a large dragon, and above them is a code... I know this code. I deciphered it when the gates of Ahn'Qiraj reopened.
But the Qiraji are long defeated... who is controlling the silithid with this? Take the Glyphs of Calling to the Bones of Grakkarond, south of Cenarion Hold. Use them there and see who shows up. They likely won't be friendly... be careful.