You can use SignHouse's signature generator, which is 100% free. You can choose between:
At the end, our Signature generator will put out a transparent-background signature that is ready to be uploaded.
A transparent-background signature works best, as that probably means you can use it in one of those rare situations where you either have a non-white background, or, on a white-background document, you still want the elements under the signature to be visible (e.g. a dotted line).
SignHouse's signature generator puts out transparent-background signatures!