Banner of Cooperation

The Banner of Cooperation is the lowest quality of the three "guild banners" that can be placed on the ground to provide an experience, honor, and reputation gain bonus to guild members (including the user) that remain within the area. Guild banners do not stack with each other; only the highest single guild banner bonus will apply. The only difference between the versions is the amount of the bonus.

Only rewards from kills receive a bonus; quests and battleground victories are unaffected. It is possible for the banner to disappear as soon as there are no targets within its area of effect.

Source
This item is sold by the following vendors for after completing the guild achievement :