What is an announcement banner?
An announcement banner can be changed by owners or moderators of the channel. The announcement banner sits at the top of every channel, and can be used to share important announcements, dates, and reminders to everyone in the channel. This can be changed at any time.
Set an announcement banner:
Click on the "i" info button at the top right of the channel. You will need to be an owner to be able to adjust these settings.
Click "Edit" and set your announcement. You can also edit your topic and description here too.
Click "Save" and you're done!