If you've got more than one email account on your iPhone or iPad, for example, an iCloud account, Gmail account, and/or a Hotmail account, or a work, school, and/or personal account, you'll probably want and need separate email signatures for each account. Thanks to iOS 6, that's now not only possible, but fairly easy to set up.
Launch the Settings app from the Home screen of your iPhone or iPad.
Tap into Mail, Contacts, Calendars.
Tap on Signature.
Choose the Per Account option.
Type out the signatures you'd like for each account, as you'd like them to appear in the Mail app.
That's all there is to it. Start a new email message and your iPhone or iPad will automatically add the proper signature to the proper account!