Here is a list of FAQ about popup announcements for Confluence.
Q: Is it possible to show/hide the pop-ups?
A: Yes, it is possible from both administrator and user.
Q: Is it possible to disable the display of announcements on a per-user basis?
A: No, It cannot be controlled by space, role, or user. The announcement will be displayed to all users who can view the relevant Confluence.
Q: Can I enable HTML tags?
A: Unfortunately, this is not implemented.
Q: Can I check if someone has read my messages?
A: Unfortunately, this is not implemented.