You're going to need a digital overlay!

The digital overlay will need to be translucent so that only the signature is seen. How you do that? Beats me. Look up the term "overlay" in the user's manual that you have for the software you are using!

You could sign them after printing them! *shrug*

It is easy.

First take out a white sheet of paper, and make sure nothing had written on it. Then you just sign on it.

After that you scan your signature into the computer. Save as whatever filetype you want.

Then use photoshop or GIMP, use the magic wand (or fuzzy selection tool) and select all the white space between your signature drawing. Delete those. You should now have your signature with transparent background. Save it as GIF.

Now open your photo that you want your signature to be included, and open that GIF file as layer. Position and resize that layer as you seems fit.

Once you're satisfied, you can just save the photo and it is ready for printing.