Footprint
From Bulbapedia, the community-driven Pokémon encyclopedia.
Footprints are literally a Pokémon's footprint. A Pokémon's footprint is displayed in the Pokédex starting in Generation II.
Dr. Footstep is a footprint expert, and can evaluate a Pokémon's happiness simply by looking at its tracks.
Pokémon Mystery Dungeon: Explorers of Time and Darkness features a mini-game where Pokémon must be identified by their footprints as part of the player's task as sentry duty.
