Hitman: Absolution HD (EP)

Silent Assassin is a a ranking at the end of a level. The very first mission you can get this is Mission 2: The King of Chinatown (since you can't get it in the prologue). The first time you can get this is in Mission 2: The King of Chinatown. To the right of the area where the target is, there is a area with chefs and they are selling food. Find the chef with the red apron (a female). Behind her is an odd looking dish with poisonous fish. After she turns her back, grab it. Now go North to where there is 2 chefs and a police guard. On the right, sneak in and find the disguise near the garbage. Walk to the middle area where the target has likely left. Poison his coffee and walk away. After he goes back and drinks the coffee, you are free to exit the level. You will also get the "Inconspicuous" achievement as well as "Whoops" if you had not already obtained it.