Greene's post in How do you bold on the Edit Alliance page? was marked as the answer
You can use the following bbcodes in messages, announcements, and alliance information:
[b]text you want bold[/b] [i]text you want italicized[/i] [u]text you want underlined[/u] [link=http://urltowhatev.er]link to whatever[/link]
However know that your total characters (including spaces, enters, etc.) cannot exceed 600.