Sigil is a 5 letter English word. It's valid Scrabble word worth 6 points. It's valid Words with friends word worth 8 points.
You can make 26 anagrams from letters in sigil (giils).
1600-10; Latin sigillum statuette, figure, stamped figure, diminutive of signum sign; see seal1
sigil, sij′il, n. a seal: a signature: an occult or magical mark.
As the sigil of House Tyrell is a rose, the sobriquet is a play on her cunning and prickliness.