There are lots of applications out there for editing PDF files, one really handy tool is adding the ability to sign forms without printing them and scanning them just to email them away again.
However not everyone knows how to make the image, it's really easy though.
As a suggestion I wouldn't save this image anywhere but a personal flash drive or in a password protected folder, since it could be used to help falsify your identity. You could sign it differently from your written signature and keep track of when you used it, you'll always know which is which and if you signed the document that way, plus if anyone gets the file they'll not be able to hand forge your signature with it.
- A scanner or camera with macro
- A pen and paper
- Photoshop or Gimp (instructions for both included)
- A PDF editor
Step 1: Write and scan
Write you signature a few times on a piece of paper with space around each one, use a black or very dark blue pen.
Now if you're scanning, use black and white mode, I used photo preset but document will likely work fine too.
Save the file somewhere.
If you're taking a photo of the signature make sure it is in focus, evenly lit and from a perpendicular angle to the paper.
For the photo takers, use black and white.