their is no option to turn it on or off, its a template modification your usercp and registration link should look something like this
PHP Code:
<if condition="$show['member']">
<td class="vbmenu_control"><a href="usercp.php?$session[sessionurl]">$vbphrase[user_cp]</a></td>
</if>
<if condition="$show['registerbutton']">
<td class="vbmenu_control"><a href="register.php?$session[sessionurl]">$vbphrase[register]</a></td>
</if>