Bounties can be placed on players in one of two ways. Either part and parcel with reporting someone for a murder, or by using the “[bounty” command. Anyone can [bounty anyone else at any time. However, it is a criminal action akin to taking an illegal contract out on someone. It is not a guard whackable action, but you become freely attackable. The minimum bounty you can place on somebody is 500 gold.
All bounties are posted on bulletin boards at every bank in the land. Should you wish to claim a bounty, simply find the offender, kill him, and bring his head to the guards. Too hard to find people you say? Moving right along…
Forensic Evaluation and Tracking allows you to use a bounty ledger. Anybody with a bounty on their head can be placed in your ledger, and anyone in your ledger can be tracked at a great distance. Something on the order of 15 times as far as just using tracking alone. Bounty ledgers can be purchased from provisioners for 1000 gold, and like spellbooks and runebooks, are not lost on death.
Forensic evaluation will not only tell you if a player is a member of the thieves guild, but also tell you whether or not that thief is perma grey, and whether or not he has a bounty placed on his head.