Thief Achievement in Dishonored
You pickpocketed items worth a total of 200 coins
How to unlock Thief
You can do this throughout the playthrough by going into sneak mode () and tapping when you're behind someone with a glowing purse on their hip. This total has to be actual coins, it cannot be items that are valued at X amount of coins. You will easily get this achievement by Mission 5. There is a big party and you are able to walk around freely stealing from everyone. No one cares and in fact some joke around and think it is funny.