The Noughts & Crosses series by Malorie Blackman is a sequence of young adult novels and a novella set in a fictional, racist dystopia.
The Noughts & Crosses series is set in a world where the people with black skin (Crosses) are dominant over the white people (noughts). The title is a reference to the game known in Britain as "noughts and crosses" and in the United States as "tic tac toe", where O represents a nought (or blanker) and X a cross (or dagger); adjusting this to an American audience would negate the pun on 'nought'. The books use first person narration, with the narrator alternating between chapters, and an X or O before the narrator's name indicates their race. Dual heritage Callie-Rose is represented by an O and X combined. - Wikipedia