Silent Sisters

The Silent Sisters are a religious order of women sworn to the service of the Stranger, the aspect of the god in the Faith of the Seven that represents death. The Silent Sisters, who have taken vows of silence, dress and prepare the bodies of the dead for funerals. Silent Sisters wear cowls that cover their heads, and veils that cover their entire face except for their eyes. To signify their holy status, they wear elaborate backbraces displaying the Seven Pointed Star, the symbol of the Faith of the Seven.

Season 1
Silent Sisters dress and prepare the bodies of Lord Jon Arryn and, later, Ser Hugh of the Vale for burial. They perform a complex funeral ceremony for Jon Arryn, involving marching in a circle around his body as it lies in state while carrying vessels filled with burning incense, and periodically turning to bow towards the body.

Season 2
Silent Sisters are seen tending the wounded as Robb Stark surveys the field in the aftermath of the Battle of Oxcross. A pair of Silent Sisters deliver a box containing Ned Stark's bones to Catelyn Stark.

In the books
In the Song of Ice and Fire novels, the Silent Sisters, sometimes called Wives of the Stranger, are considered holy and inviolate. They wear grey cowls which hide their faces apart from their eyes. There are some internal monastic orders that septons (male clergy) and septas (female clergy) can belong to. However, the Silent Sisters are an entirely distinct organization from septons and septas within the Faith of the Seven. The Great Sept of Baelor even has three separate entrances for septons, septas, and the Silent Sisters.