Official rule text
50.1 The leader slots of the leader sheet are where players place their three leader cards during setup. Each slot displays the name of the type of leader that is placed in that slot (agent, commander, and hero) as well as a symbol in the upper-right that helps players quickly determine which side of those leaders begins the game faceup. a The sides of the leader cards that display one (agent), two (commander), or three (hero) hash marks, respectively, begin the game faceup.
View official source
Source: Living Rules Reference and FAQ - Prophecy of Kings
Expansion: Prophecy of Kings
Version: 2.0
Reference: Rule 50.1