This request could be achieved via 'Project status', which will show a message in both web and developer.
ACTION:
- Login to the project on Developer side, chose the target project and then navigate to 'Administration' menu on Developer toolbar
- Navigate to Projects -> Project Status, input custom message (e.g. 'This is for testing')in the 'Enter Project Status' filed, and make sure the option 'Display project status' on the bottom is checked.
- In the 'Project Status' window toolbar, navigate to View -> Editor Header, delete message 'Project Status' in the input filed.
- Under View -> View HTML Source, delete messages in the content field.
- Save all changes and go back, re-login on web, the change will work.
Outcome screen shot: