L for Longhorn. They changed L to F since Longhorn was long dead, and Vista actually had little to do with it. Old scheme involved (W)histler - (L)onghorn - (B)lackcomb, then they switched to numbers and corresponding letters for code names. C and S for client/server build. HB/HP/PR/UL - editions of Windows 7 In Windows 8's case the label would be something like HRMCxxFRER_xx_DVD, but the naming scheme can change again, as you can see.
im downlaoding the torrent now and seeding it off a seedbox, will confirm if its fake or real within the hour