Yes, this is an annoyance for some people and I am going to make it an option in the future.
To remove it you need to edit a PHP file.
First make a backup of your site or at a minimum, just the file /wp-content/plugins/speakout/includes/emailpetition.php
Now open that file in an editor. If you use cPanel open it in the file editor.
At about like 635 you will find
<p class=”dk-speakout-caps”>%%’ . __( ‘your signature’, ‘speakout’ ) . ‘%%</p>’;
Remove almost all the line, leaving just the last 2 characters
‘;
save the file. That should do it.