Moon letters

From the One Wiki to Rule Them All, the Lord of the Rings Encyclopedia.

Moon letters are special runes written in silver ink with silver pens. They were created by the dwarves in a cunning fashion as they can only be seen by the moon of the shape and season on the day they were written. They are only mentioned in The Hobbit when Elrond held up Thror's map to read to Thorin and Company