Change the "From" name in confirm signature email

There is a setting for this that you can change on the Email Petitions “Settings” page. Under the “Confirmation Emails” tab, change the value of the field labeled “Email From” to the name and email address you want in the format:
Website Name <email@address.com>

A Quick explanation of how this all works:
When you first install the Email Petition plugin, the confirmations’ “Email From” setting is created for you automatically by pulling your site name and administrator email address as they are found on the Settings > General page in the “Site Title” and “E-mail Address” fields. In order to customize the from address for confirmations after the plugin has been installed, you must follow the instructions in the previous paragraph.