Dust Longhand

Once upon a time, one Richard Gorman of the Forest of Pain accidentally (in official terms, but more likely deliberately) used necromancy on his family's crypt. He failed utterly, only bringing them back as ghosts, and not very well attached ones at that.
What he also did was give their bones particular qualities that lend themselves very well to communication with the newly departed. When ground and left to fly into the air, the dust will form into their own alphabet.
It took time to determine what exactly the letters meant, scrambled as they were between this world and the dimension of ghosts, but eventually scholars worked it out. In some of the graveyards of the world, they still make use of this script.