Just to share some info for this:
I used to do this sort of thing quite a bit. What I used was a scanner to scan my hand written signature to an image file. I would then paste the image file, which supported transparency, over the signature line. More recently, I used Photoshop to draw a signature saving in a transparent image file.
Just to warn you though: you are asking for legal advice, and you are not going to get that here. I would consult with an attorney to find out exactly what is legal.
What you're describing is known as an e-signature. There is not a form field that you add for this, but someone with Reader/Acrobat 10/11 can use the EchoSign tools to add a hand-drawn signature. For it to be legal, you should use the EchoSign service, which is not free.
This does create a problem for data extraction though. After a document is e-signed, the form fields are flattened, which removes the actual fields and leaves their appearances, so the data isn't easily extracted is it is when the fields are not flattened.