What is an announcement banner?
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!
Your announcement will be displayed right below your channel information at the top, in a blue banner. You can change your announcement at any time!