You can say "What's your sign?" but that makes you sound like you're trying to hit on someone AND that you're stuck in the 1970s. People who ARE into this usually ask what your birthday is, and then say "Oh, you're a Gemini," because they KNOW the birthdays and the signs.
It's almost always Aries, Taurus, Leo, Libra, etc. Sometimes a colun in the newspaper m