Hi Pete -
The service key for Samsung registers has a 'C' stamped on it. That is the key that will let you get to the 'S' position. If you don't have one, you have three options:
1) Contact a dealer in your area to see if they will give/sell you one.
2) Find someone who owns a Samsung register (any model will do, all of the Samsung/Sam4s registers made over the last 15 - 20 years use the exact same keys) who has a 'C' key and see if they will loan/sell/give you one of theirs.
3) Depending on how mechanically inclined you are, you can make a make-shift 'C' key from one of your other keys. Looking at the key, going from the tip toward the head, you will see first three little teeth, then you'll see a 'fin' (whose width varies depending on the type of key, narrower on the 'P' and 'C' keys, wider on the 'Z' & "REG' keys) followed by a 'notch' that is about 1/16" lower than the fin and finally the neck and head of the key. To make a 'C' key, you need to file or grind off the fin down to the same level as the notch, being careful not to mess up the three little teeth. A key thusly modified will let you get to the 'S' position, one click clockwise past the 'P' position so that you can MAC the register. BE CAREFUL not to turn the key any further clockwise than the 'S' position.
Good luck ...
Steve
July 2010