Indicates the type of server or audio stream. The 'Globe' symbol indicates a plain-vanilla HTTP server. In that case, some options will not be available such as the 'WWW' button and bitrate display.
The 'Lightening Bolt' symbol indicates a ShoutCast server. This server supports WWW pages and displays the correct bitrate.
The 'Real' symbol indicates that the HTTP server is sending a RealAudio stream. Not to be too confusing, Streamer is not a RealAudio client. Although it will parse .RAM files and recognize the x-pn-realaudio MIME type, it can only get files using HTTP (and not PNM) and play Really old 2.0 RealAudio files.