I don't think emoticons work for astrological signs. Just use the unicode ones or their Pestercum handles. ♋ ♈ ♉ ♊ ♌ ♍ ♎ ♏ ♐ ♑ ♒ ♓, if you need em.
That said, Fef is definitely Superfast Jellyfish (Both in the fish theme, and the mood of the music vs. the mood of the actual content), I'm of the opinion that Aradia is more of a Dirty Harry (Hard to explain) type person, and that Clint Eastwood should go to Gamzee (It's just like a fucking glove. He is definitely happy and mostly feeling glad). Methinks Karkat would best be suited by Kids with Guns (Same deal with Dirty Harry, probably interchangable. It just feels right.), Stylo for Equius (The funk suits him.), Fire Coming out of the Monkey's Head for Sollux (The doom thing, as well as the there's some parallel in the sort of disconnects from society they both had.), Nepeta gets 19-2000 (It's just kinda upbeat and playful.), Rock the House and Vriska fit well enough, I want to say Feel Good Inc for Tavros (A, it has to be *somewhere* on the list, and B, Tavros had it pretty bad and the world just kinda went to shit around him), I guess El Maņana for Kanaya (She strikes me as the one sane soul left, and her role seems to be watching everything break down crazy shit), and to round off the list, Terezi with, I dunno, Rhinestone Eyes? I just can't really think of one that fits her especially well.
So, to do the list in your format:
♋-Kids with Guns
♈-Dirty Harry
♉-Feel Good Inc.
♊-Fire Coming Out of the Monkey's Head
♌-19-2000
♍-El Maņana
♎-Rhinestone Eyes(?)
♏-Rock the House
♐-Stylo
♑-Clint Eastwood
♒-Melancholy Hill
♓-Superfast Jellyfish