As a typical example of how trying to second guess Hickman sends us down rabbit holes. It turns out that although the greek letter Theta is usually written as Ɵ it originated as the Etruscan symbol which is our familiar cross in a circle.
Then, not only do we see this in the X on the cover, it also crops up in upright form on the page with the fortune teller:
teller.jpg
and is repeated when Moira appears.
And then when one notes that the tarot cards are visible, one wonders if this specific all seeing eye symbol is important. Especially as the design is echoed in the fortune teller himself.