The Kings Couriers are members of the Diplomatic Corps. They are usually women because they are known to usually have more tact then men who often tend to use 'muscle' rather than 'brains' at certain times.
Couriers sometimes have dangerous assignments and therefore have to know how to defend themselves. They use a long knife which are usually concealed somewhere on their person. They also sometimes travel in disguise which is what Alyss does in The Sorcerer in the North, she travels under the guise of Lady Gwendolyn.
Alyss was revealed in The Burning Bridge, to be wearing the 'simple, but elegant' white gown of the Couriers, with the bronze laurel branch pin, the symbol of her authority, fastening a short blue cape at her right shoulder.
In a letter to a fan, John Flanagan stated regarding footwear: "Couriers do a great deal of travelling so they'd wear light calf-high boots, suitable for riding, with flat heels."