Royal letter of safe conduct

This is a quest item, and so far I have found two of them during the game:
 * 1) You receive this letter from Triss Merigold when chapter 3 is started
 * 2) You recover one from Gellert Bleinheim during the The Viziman Connection quest

The letter says:
 * The bearer of this document is by the will of Foltest, King of Temeria, etc. allowed to be on the streets of the city of Vizima after nightfall, regardless of any regulations. He is also beyond the restrictions applied during the state of emergency.

The letter is signed by Foltest.