User blog comment:The Dragon Demands/Season 3 Blu-ray extras announced: Histories & Lore featurettes/@comment-8331-20140129215248/@comment-8331-20140129220613

Yes... several sigils have been established by Martin in e-mails and letters, like the words of the Boltons being "Our Blades are Sharp". The location of  Clegane's Keep comes from the map in the HBO site while the books never mention it.