Is there a way to make announcement in zipboard for all project in the organisation?
Yes, For enterprise plan there is an option to add an announcement.
Steps to add an announcement
1. Log in to your account
2. Click on manage org from the profile on the top right corner
3. Navigate to Announcements
4. From Announcement page--> click on ADD to add an announcement
Added Announcement will be shown on all pages and for all collaborators and clients. One Announcement can be added at once if you want to add a new announcement, old one will be replaced.