Ubi's Splinter Cell promotion has already awarded a theme, a trailer, and stills. According to the forum following the craze, different assortments of prizes have been awarded for plugging in the final code both with and without successfully entering the previous three codes. Some participants received a code for the Akali character skin as well as one of at least two different guns, while others received only a code for the skin.
My own email inbox included a message with the following title:
+++ codeofconviction Reward | 2/3 Inputs = VR Alkali Skin and SC3000 +++
The content below included a code that apparently must be entered in-game once the title releases:
>>>>>>>This code is for Splinter Cell Conviction on Xbox 360<<<<<<<
>>>>>>>Code may only be used once<<<<<<<
>>>>>>>From the Menu, select EXTRAS then EXCLUSIVE CONTENT. Select REDEEM CODE to enter your key<<<<<<<
>>>>>>>Once it is validated, the skin will be unlocked. You can check unlocked items from the menu<<<<<<<
>>>>>>>High speed internet connection required<<<<<<<
>>>>>>>Maintain your conviction<<<<<<<
So the mystery is solved. Those who exhibited the conviction required to follow the promo until the end were ultimately awarded with a character skin and possibly a unique in-game weapon. Not too bad a haul for a little investigative work. Sam Fisher would be proud.