This is rung in the Assassins' Guild when a contract is announced, notifying senior assassins that there is a killing to be made - literally and figuratively.
Possible reference to the Division Bell of Roundworld that is rung in or around a parliament to signal a division and thus call all members of the chamber so affected to vote in it. Once sounded, members in the Commons or in the House of Lords have eight minutes to get to the appropriate Division Lobby to vote for or against the resolution.
There is also the Lutine Bell in Lloyds of London (Maritime Insurers) which was traditionally struck when news of an overdue ship arrived - once for the loss of a ship (i.e. bad news), and twice for her return (i.e. good news).