- last post: 01.01.0001 12:00 AM PDT
Sierra is the universal phonetic alphabet call sign for 'S'
and it has been said by Bungie before that Sierra is a callsign for 'Spartan'
Sierra 117 is the first level in Halo 3, referring to S-117:John.
S-259 and S-320 are mentioned in that trailer, even though the Spartan number ended at 150 I believe.
Also, the Spartan III's callsigns were allocated in the format:
1 number followed by three letters. so, A001, B292 etc
So we know they aren't Spartan III's.