OK - you can do this on a desktop computer or laptop in your same AdobeID account on https://cloud.acrobat.com/fillsign and then that imported image will be available as your signature in the Fill & Sign iOS app assuming you sign in with the same AdobeID.
In the web app ttps://cloud.acrobat.com/fillsign you have choices of a typed text signature in a choice of fonts, a drawn scribble signature (like in the iOS app) and importing an image.
The data/forms etc are shared across platforms using the same account so if you create the new Signature in the web it will be available on your iPad.
Thanks,
Josh