find the following lines in admin/sendemaillib.php file:

  if (!EMAILTEXTCREDITS) {
    $html["signature"] = $PoweredByImage;#’

‘;
    # oops, accidentally became spyware, never intended that, so take it out again :-)
    $html["signature"] = preg_replace(‘/src=”.*power-phplist.png”/’,'src=”powerphplist.png”‘,$html["signature"]);
  } else {
    $html["signature"] = $PoweredByText;
  }
  innovita edit

Comment these line out and replace them with this:

$html["signature"] = “”;

Alternatively, edit config.php

change

define(“EMAILTEXTCREDITS”,0);

to

define(“EMAILTEXTCREDITS”,1);