Finally got round to getting an image of Ms Hawkings broach.
The Ouroboros, also spelled Oroborus, Uroboros or Uroborus (IPA: [ˌjʊərəʊˈbɒrəs]), is an ancient symbol depicting a serpent or dragon swallowing its own tail and forming a circle. It has been used to represent many things over the ages, but it most generally symbolizes ideas of cyclicality, primordial unity, or the vicious circle. The ouroboros has been important in religious and mythological symbolism, but has also been frequently used in alchemical illustrations. More recently, it has been interpreted by psychologists, such as Carl Jung, as having an archetypal significance to the human psyche.
The name ouroboros (or, in Latinized form, uroborus) is Greek οὐροβóρος, "tail-devourer". The depiction of the serpent is believed to have been inspired by the Milky Way, as some ancient texts refer to a serpent of light residing in the heavens.
Source: Wikipedia