Site Header
From the 'My Site' page, click the 'Site Header' link in the menu, which will open the editor screen..
What you see below is that for the header we've inserted an image, but no text. Ok its an image of text, but it is an image we created. You can enter text or an image, or both, but for the sake of your guest you will want to keep your header small enough to be appropriate for a site header.