hello !

i know just a little about this, because it's really not important in my opinion. so :

ed -> Nikon, low distorsion lens, because of special treatment
usm -> canon, ultrasonic motor in the lens for af
af -> autofocus
dc -> sigma, lenses for digital body
ex -> sigma, expert lens (high quality)
'                 ' -> leica, they wrote nothing on their lens because they are just perfect  lolllllllllllllllllllllllllll

hope this help ;o)
Olivier