I would sign with a big pen so the scanned image is huge, then make it smaller from there.
Use plain white paper and use something simple like a black pen.
Edit the image after you've scanned it and delete all the white. Whether you want to use anti-aliasing is up to you when you do it, probably not a bad idea.
You may want to make sure all the black is truly black, but it doesn't really matter. It can just make color replacing easier later on.
Save it.
Then just open it up and copy it to a new layer on the picture you want to put it on. Be sure to scale it appropriately.
You can easily adjust the color of it, add effects such as embossing or a pillow effect, or whatever you want once it's on the new picture.
b