Scents appear when at the location where someone commits a Crime. They look like exclamation points bobbing up and down and can only be seen if you Toggle Tracking.
Scents can be gathered to obtain Evidence and used to track down the perpetrator, his or her home base, or the item stolen, if applicable.
Few Scents are not summonable, but most are, if you commit a summonable crime and other players get access to your Evidence, they can summon you online at your homestead and kill you, or put you at the Stocks (See Crime & Punishment)
Each scent gathered provides 180 minutes of tracking time.
Scents based on the crime committed:
Trespassing: left when a player tries to cross a hostile claim, or use a door, gate, or chest on that claim. You can cross/enter/leave a hostile claim without learning the Trespassing Skill. Trespassing is not summonable and leaves no Evidence. Trespassing scents expire after 1 day.
Assault: left when one player initiates combat with another player. Assault is not summonable and leaves no Evidence. Assault scents expire after 1 day.
Battery: left when one player knocks out another player. Battery is not summonable and leaves no Evidence . Battery scents expire after 3 days.
Larceny (Theft): left when a character tries to take anything off a claim they don't have permissions on (such as out of a chest, carry an object across the claim borders), or loot a body (leaves no scent if it is your direct ancestor). Larceny scents expire after 9 days.
Waste: left when a character attempts to destroy or build anything on a claim you don't have permissions on. Waste scents expire after 11 days.
Murder: left when any character is killed by another player. Murder scents expire after 16 days.
Forgery: left when any character mint Silver Bars into Silver Coins. Forgery scents expire after 5 months.
Aggravated Assault: left when a player breaks the bones of a KO'ed player (beat face) or when injecting drugs. Aggravated assault scents expire after 3 days.
Poisoncraft: left when a player crafts poison darts with the Blowdarts skill. Expires after 5 months.
Revenge: left when a player uses an Evidence to murder a knocked out criminal. Expires after 9 days.
Witchcraft: left when a Witch tries and fails to attune a doll to a player. Otherwise, Witchcraft leaves no scents and so it is most dangerous to stand still in a public place and give a Witch a good target for attuning. Witchcraft scents expire after 17 days.
See the page on Crime & Punishment for more details.