well Syd is sort of a nickname already...hehe, but another one for her would be Andromeda...because in roman and greek mythology she was the daughter og CASSIOPEIA (who is somewhat like Jack), she was punished for her mothers vanity (she was held at the CIA about a prophecy that turned out to be about her mother supposedly). Then PERSEUS saved her from her fate (Vaughn saved her by taking hr to mt. subastial spl.), then she married Perseus. (vaughn and syd are now dating)...
the story of Andromeda somewhat reminds me of Syd...