The kesiera is a piece of jewelry worn by Cairhienin noblewomen. It consists of a jeweled pendant on a chain. The chain is secured into the woman's hair with the jewel hanging on the forehead (NS, Ch. 12).
"She wore a small stone on her forehead as Moiraine had so long ago, though Daigian's was an appropriately white moonstone. The tradition apparently had something to do with being a Cairhien noblewoman, as did the four colored slashes the woman wore on her dress." (Nynaeve thinks about Daigian; The Gathering Storm, Chapter 7)