Hitman HD Pack

To get a SA rating, you must aim to kill the target and the target only, on a near perfectly discreet run. SA ratings can be earnt on any level.

Below is the criteria for SA ratings, taken off the official Hitman forums :
No non-accidental deaths other than targets.
No non-target NPCs were wounded while alive.
No bodies found.
No covers blown.
No witnesses left alive.
You are not caught on camera.
No weapons were found on you during any searches.
You exit the mission with all custom weapons you started the mission with (by either carrying them with you or storing them in an ICA crate).

If you do not violate any of these, you will achieve an SA rating.

NOTE - However, it seems to work on a "point" basis. For instance, you can be spotted (alert) and still get SA. I can also confirm you can kill at least one guard. I killed a guard on level 4, as well as the target, and hit an SA rating. I do not think you can kill 2 guards, this awards you professional.

Below is a video of SA on the first 'true' level - Anathema (This is not my video)

For those who want text -

* Run straight ahead, and knock out the guard when he passes through the door ahead of you. Take his clothes. I suggest dragging him away from the door. You don't want him here later.
* Run into the grounds, turn right, and enter the basement. Go up the stairs. Watch out for the patrolling guard in the kitchen.
* Use the stairs in the kitchen to go to the second floor.
* Use the door straight ahead of you. From the balcony, walk around the ledge to the roof.
* Cross onto the bosses balcony.
* Wait for boss to enter his office. Sneak behind him, and kill using fibre wire.
* Take the bosses key.
* Go back the way you came, all the way to the basement. Open the locked door with the key.
* Leave using the exact same route you entered with.

You can complete the first level of Contracts: Asylum Aftermath easily on any difficulty; and be awarded a Silent Assassin rank. Just remember to watch out for the orderly workers in blue with tasers on the 1st floor and if you do pick up a weapon pocket/conceal it before using the elevator.

--From the start pick-up the car key from the body in front of you.
--Follow the maze of the asylum to the elevator.
--Take the elevator to the 1st floor.
--When the elevator stops exit and turn to the left going through the doors with the long bars. Proceed straight back to the small rooms and enter the one with a green light above it (as opposed to red). Once inside you can change costume into a patient gown.
--Exit the small room going back through the door with the bars you came in, keep going straight and run into the room with the police in tactical positions.
--Enter the room on the left behind them and wait for the police officer patrolling to return from the spiral staircase. Follow him until the upstairs room doors shut and hide behind them. Once he leaves to go back downstairs you can sneak behind him and enter the room.
--Exit onto the balcony and climb down the ladder. Be careful not to walk off the balcony or fall off the ladder, and watch the police officer walking a circle next to the black getaway car. You'll have to go down the ladder and sneak on the ground to the car, and quickly escape using the action button.