friendica-addons/pageheader
..
lang
templates
pageheader.css
pageheader.php
README

Page Header

For server admins only.
Displays a text message for system announcements'
The message is entered in the admin account at settings, Addon settings.

If you want to use HTML in the pageheader, create a file called pageheader.html 
in the document root of your friendica instance and add the html there.