I'd have to slightly disagree with Joe...
It only makes a difference if you believe it does.
That actually sounds a lot like how flirting works: you just have to
know that you're good at it,relax, and hey presto, you're good at it.
Zodiac signs, along with most mysticism, homeopathic medicine, and psychic mind readers, work through the placebo effect. This is a mental effect where your beliefs cause your body (or your behavior) to change -- and it's a well-researched scientific phenomenon.
So, to sum up: if I were you, I wouldn't give it a second thought, because then you won't need to.
Some info, if you're interested:
Wikipedia's page on the issue
An article about it in a scientific journal