When you have chosen to support Zaros in the emissaries activity by speaking to Soran, the basic version of the banner of Zaros will be your reward.
The basic banner is used throughout the activity to complete the jobs you are asked to do. Completing each set of jobs will gain you an upgrade to the banner in the form of three boosts, one for each set of jobs. The boosts can be activated once a day and last for one hour. The boosts are:
Combat boost - temporarily boosts your Attack, Defence, Strength, Ranged and Magic levels by 5
Skill boost - temporarily boosts one of your choice in the following skills by 2 levels: Fishing, Mining, Runecrafting, Crafting, Woodcutting, Firemaking, Fletching, Construction, Hunter, Thieving, Cooking, Herblore, Farming
Exploration boost - temporarily boosts your Agility level by 2