So the plus is hardcoded in the html. This is the html of the 'Create New Moderator Button':
Code:
<xen:topctrl>
<a href="{xen:adminlink 'moderators/add'}" class="button">+ {xen:phrase create_new_moderator}</a>
</xen:topctrl>
And this is the html of the 'Create New Administrator Button' from the admin_list template:
Code:
<xen:topctrl>
<a href="{xen:adminlink 'admins/add'}" class="button">{xen:phrase create_new_administrator}</a>
</xen:topctrl>
As you can see there is a + missing.