Not using the stock Mail app, no. There might be an app (or two) in the App Store that allow you to create such a signature, but I don't know of any off the top of my head.
I know this is probably a bit of a kludge, but can you build a signature in, say, a word processing app or Evernote (or some such) and then attach it to your e-mail via cut and paste? Or, have the image on your iPad and then send the e-mail from your Photos app and attach that picture?
As you can see, I'm just throwing ideas out there. Sorry to not be of better help.