How to remove the default e-mail signature on the Kindle Fire
Does the world really need to know that you sent an e-mail from your Kindle Fire? We'll show you how to remove the default signature.
Step 2: Under the "Sending mail" section, select Composition defaults.
Step 3: Remove or edit the signature from the text box. If you prefer to turn off signatures, uncheck the Use Signature box.
That's it. If you're considering keeping the signature, read Al Sacco's post at CIO.com on why you shouldn't.