OMG, I love threads like this.
Anyone watch Star Trek: Deep Space Nine? It's one of my favorite shows, and even though a lot of the characters weren't born on Earth I like speculating about their signs.
I always thought that Gul Dukat had to be the bad type of Leo, like Mussolini. The actor who plays him is a Taurus, but the character himself gives me Leo vibes.
Garak is a Gemini or a Libra. With a moon in...Scorpio?
Captain Sisko could certainly be a Scorpio. He's very complex and intense and not above playing dirty when he needs to.
Major Kira is...a Taurus?
Dax is a Sagittarius.
O'Brien is canonically a Virgo, I believe. Which makes sense, although I see him having prominent Cancer placements (perhaps Cancer rising).
One of the novels says that Bashir is also a Virgo, but I REALLY don't buy that. He's pedantic, detail-oriented, and wants to help people (not that that's all Virgos are!) but he's also way more outgoing and fantasy-prone than any Virgo I've ever met, and he really wants to be a hero and live a dangerous, glamorous life. So I'm gonna say he's an Aries with a Pisces moon, or some such thing. He might be a Leo rising.