Create Favicons
favicon.ico (short for "Favorites Icon") is the graphical icon that is displayed on the URL bar and bookmarks list on some browsers, originating with Internet Explorer. It's a nice, unobtrusive way to impress branding outside the page area. This site uses a site-wide yellow letter b.
This article describes how to create one on a Mac. For Windows, Linux, and others, the free png2ico utility can convert PNG files to the required format.