The album's logo is Vesica piscis, or Venn diagram of two sets, presumably the real world and the hidden world.
The shape Vesica piscis has a major axis: minor axis ratio equal to the square root of three, this can be shown by constructing two equilateral triangles within it.
The cover of the Chalice Well in Glastonbury (Somerset, United Kingdom) depicts a stylized version of the vesica piscis design (see picture).
It is the symbol of the Catholic University of Leuven, in whose seal it is enclosed in a vesica piscis shape whose margin bears the text "Universitas catholica Lovaniensis. Sedes sapientiae" (Latin for Catholic University of Leuven. Seat of Wisdom).