I've been asked this question more than once and thought this was the best way to deal with it. In the Hall of Kings' it is Deathbringer in the runestone on the highest dais, its apparition is used when it wants to communicate while in the stone. Deathbringer has specific responsibilities within the Hall of Kings, one of which is the ability to communicate and appear as an apparition. Red Rose and Black Rose are the least powerful of the Runeswords and their runestones are in fact lower than the rest. Timekeeper is the most powerful of the Swords of Law. Remember Deathbringer was before the law. There are eleven total Runeswords, of which six are either mentioned or introduced in ToS. So that means you will hear about two others.
I am working on a story called 'Runeswords', that is set at the very beginning of Andor and feature the "Three that are One". All the Runeswords are discussed, actually the story follows the forging of the Nine. A spoiler; the Roses were not forged by the same being that created the Nine, but they were forged in the same manner and are under the law.