Ingame I can write a note to the exact hand by clicking "N":
This feature is not intended to mark the hands but it is used to write notes for the player.
Actually, by clicking "N" you insert a short visual representation of a hand into a Notes Container for an exact player instead of describing this hand in words:
And then you can see these notes by hovering a mouse over Notes Icon in your HUD:
In the same way, you can insert a hand into a note while not playing:
And advanced hand marking feature will be implemented later: