Assassin's Creed Chronicles: China

When an enemy is aware of your presence their line of sight will turn red and an 'alert' notification will appear at the top of the screen. Under this notification will be a timer of 10 seconds. Once this reaches 0 the guards will no longer be alerted to your presence and their line of sight will return to white. At this point you would have successfully escaped an 'alert'. Once you do this 30 times the trophy will unlock.

You can farm these at any point in the game as long as you can easily get to a safe location once an enemy has spotted you. An easy location to do so is during Memory Sequence 3: The Port. See the following video by Aylown Dot for the exact location: