Look for the following in the vB FORUMHOME template and edit as desired:
Code:
<if condition="!$show['guest']">
<!-- member logout -->
<td align="$stylevar[right]"><a href="login.php?$session[sessionurl]do=logout&logouthash=$bbuserinfo[logouthash]" onclick="return log_out('$vbphrase[sure_you_want_to_log_out]')"><phrase 1="$bbuserinfo[username]">$vbphrase[log_out_x]</phrase></a></td>
<!-- end member logout -->
</if>