By default, the signature for your iPad email just says you sent it from an iPad. But you can change your signature in Mail. Here's how to customize it.
Navigate to Settings >> Mail, Contacts, Calendars, then tap Signatures.
Type in the signature you want to use. Then close out of Settings.
Now when you send an email from your iPad, recipients will see your new custom signature.
Note: This also works on Apple's iPhone and iPod touch.