Places a small note with an optional link at the top of the admin pages.
The Admin Header Note can be positioned and colored using any CSS unit (http://www.w3schools.com/css/css_units.asp), including %, in, cm, mm, em, ex, pt, pc, and px, for positioning, and color name, comma separated RGB values, comma separated RGB percentages, or HEX number for color. Check above link for examples. Coordinate origin is the upper right corner.
In the link field, it is incumbent upon the user to supply a valid URI, absolute or relative. A relative link must use the WordPress site root.
The message field will accept text of any length, but anything over a few words will be difficult to position neatly.