Ghoulinda advised me to be on the lookout for what she called "Unpowered Crone-Speak Runes". She also explained, that in order to empower them, I would need to push fleeting life energy through them. To do this, one must end the life of a being, and at the time of death, the life energy will pass through the rune. When enough energy has passed through the rune, it will become empowered.