Hi Dave,
shen: Hieroglyphic symbol depicting a circle or ring of rope folded and knotted at the bottom; since the circle effectively had no end, it came to denote infinity. When the shen sign was depicted encircling the sun, it appears to have symbolized the eternity of the universe. This property of encirclement was extended to denote protection as well as eternity, making the sign doubly potent.........is particularly associated with Horus the falcon or Nekhbet the vulture who hold the sign in their claws above the king, offering him eternal protection......." (BM dict. of AE 1995: 267)
According to J.P. Allen, Snw, 'circle' refers to the circle of the world, and the combination of the Snw with the king's name inside it originally indicated the king has dominion over the whole world. (Allen 2001: 65)
"In MK and NK inscriptions, the cartouche or shen 'ring' reflects the phrase 'all that the sun disk circles (shen)'" (Quirke 2001: 123)
A fragment of an ivory box panel from the Dyn 1 reign of Den has the S12 'gold' sign with the shen-ring (Snw) beneath it, next to Den's Horus name, 'Horus Den' (Hrw dn). The appearance of the shen ring here brings to mind the sun or full moon on the horizon - a circle on a horizontal 'bar'.
In Netjerikhet's Dyn 3 funerary complex, Horus the Behdetite appears above Netjerikhet, extending to the king a protective emblem in the form of a shen ring. (ref. C. Muller-Winkler, 'Schen-Ring' LÄ V, 578)
CT