That is the {$lng.eml_signature} variable. You can erase it under 'languages' or remove it entirely by editing mail/html/signature.tpl.
The header link is this line of code in head.tpl:
<td class="HeadLogo"><a href="{$http_location}/"><img src="{$ImagesDir}/xlogo.gif" width="244" height="67" alt="" /></a></td>
Moving to template editing.