From publisher blurb:
Though runes and symbols are not generally thought of as evil or dangerous, some symbols evoke fear, danger, and ruin. Ruinous Runes are the work of evil forces that have harnessed the power of symbols tied to dark forces. They may use them to spy on enemies, create sleeper agents, subjugate champions of good, or create ticking time bombs.
Ruinous Runes are magic items that are inscribed directly onto the body, and these four examples expand on the concept of evil runes as presented in the Pathfinder Roleplaying Game.