The PCs have been traveling for a long time down the same stretch or round with no sign of anything suspicious. As they cross over to the next hill they see a gigantic splater of blood with a bleached dragons scull in the center of it. It the dragon skull's mouth is a tattered backpack with something wiggling inside of it.
MoonInk: This alchemical product has 101 uses. The Ink/Paint dries to be totally clear and almost unnoticable. Under moonlight, it comes forth as a silver ink. It was originally used by the Elventi to enhance certain pieces of art. It is used by espionage types to produce secret messages, nobles for hiddle plots, and diabolical cultists to write their spell books (usually in books of holy texts, to throw off people reading it).