Perform the following tasks in the Assassin Guild Challenges:

Signal Assassin Recruits during a fight twenty five times. Note: This must be done when Guards are actively fighting you.
Use Arrow Storm fifteen times. Note: This is only available when you have three Assassin Signals.
Twenty Assassin Recruits signaled to kill a target.
Five Assassin Recruits signaled within a Core Memory.
At least 5 recruits raised to the rank of Assassin (level 10).