Fill the missing square.

[![enter image description here][1]][1]

It is my own creation.  It is not part of a test, so there is no ABCD choice.  You must figure out the missing pattern.

Before you ask: nothing to do with noughts and crosses (aka tic-tac-toe).

Hint:
>! The key is in the title.

  [1]: https://i.sstatic.net/pXDis.png