As a faction agent, you have access to a secret network of supporters and operatives who can provide assistance on your adventures. You know a set of secret signs and passwords you can use to identify such operatives, who can provide you with access to a hidden safe house, free room and board, or assistance in finding information. These agents never risk their lives for you or risk revealing their true identities.
Use the tables for the acolyte background in the Player's Handbook as the basis for your traits and motivations, modifying the entries when appropriate to suit your identity as a faction agent. (For instance, consider the words "faith" and "faction" to be interchangeable.)
Your bond might be associated with other members of your faction, or a location or an object that is important to your faction. The ideal you strive for is probably in keeping with the tenets and principles of your faction, but might be more personal in nature.