Yes, you've seen this in Wikipedia; the fake MediaWiki interface. Want it? Read it.
To create one Edit
First, you'll need to start with the div syntax:
Next, choose class="usermessage".
Now, enter your text. We'll go with the one above:
<div class="usermessage">You have [[User:Blow of Light/Played!|new messages]] ([[User:Blow of Light/Played!|Last change]])
Finally, end the message with </div>
Then, if you get it right, you'll get the message above:
On Wikia, you'll find more bizarre headers, like this: