When you join a server, your online nick is shown which is then followed by your account name in brackets. Also, you can see the account names in the names list if I remember right, it just takes the right button press, as to which button escapes me at this moment
When the list of names is shown, hold Ctrl+Shift to display account names instead of display names. This applies to S1 and S2 licenced servers only, of course.