Signaling Snare

A subtle snare used in hunting or tracking, a signaling snare often consists of carefully prepared earth, piled sand or stones, specific arrangements of vegetation, and so forth. When a creature enters a square of a signaling snare, nothing happens to the creature, but instead it causes a small, unobtrusive disruption to the terrain that allows the snare's creator or another creature who knows what to look for to determine whether a creature of the appropriate size entered the square.