In Stairway To Heaven, Oren, Constantine and Tessa used this under brainwashing from Metatron to kill rival angelic faction leaders to bring their followers under his leadership rather than Castiel's. Gadreel later used this in Do You Believe In Miracles? to free Castiel from Heaven's dungeon, sacrificing himself to do so. This (as well as many other new sigils) have only been shown in season 9, so it is possible that they were hidden from all the angels with the exception of Metatron and might have been written on the angel tablet.