How To Define A Signature Style
It all depends on what you stand for, literally. If, for example, you stand for women's rights then the obvious choice would be to find a type of style that makes you stand out at all times, so that it is impossible to ignore you. This could be brightly coloured hair, obviously big earrings or even a specific colour of clothing.
At the end of the day, the style you choose must not contradict and reduce the effectiveness of your message.