Please drop the vacuous starsign entry on actor info page. It's embarrassing. Belief in astrology is the same as belief in unicorns and santa. It is superstitious and ridiculous and embarrassing and you should grow up.
As the original poster indicated, the Star Sign is indicated for a person when that information is available. It is displayed towards the bottom of the page. For instance, IMDb indicates on Gemma Arterton page [http://www.imdb.com/name/nm2605345/]:
Star Sign: Aquarius
As much as I consider this a silly piece of information to include on IMDb, I seriously doubt that IMDb will remove this information from people pages. Ranting about it is unlikely to positively persuade IMDb to remove Star Sign information. The astrological star sign has been provided by newspapers as entertainment since the 1900s. There is a market for this kind of pseudo information and IMDb is simply meeting that need, no matter how absurd it may be.