If you're not interested in telling everyone you sent an email from your iPad, you can delete or change the default signature that is appended to the end of messages.
1. Navigate to Settings -> Mail, Contacts, Calendars -> Signature
2. Press the Clear button to remove the signature. If you wish to enter your own, use the keyboard to input text. When you're finished press the Home button to exit.
You now have a custom signature, or none at all.