Apple have made it extremely easy to sign your documents. Provided you have OS X Lion or newer, follow this simple guide to create your very own digital signature using your built-in iSight/FaceTime camera.
Create your signature
First, launch Finder and select Applications. From your list of applications select Preview.
Go to Preview at the top of the window and select Preferences.
Navigate to Signatures and click Create Signature.
Write your signature on a piece of paper and hold it up to your iSight camera. Using the Signature Preview window on the right, ensure your signature fits in the allocated space and is nicely lined up. Ensure that you are in a room with plenty of light and use a crisp white piece of paper and a black pen for best results. Click Accept when you're ready.
You will now see your signature listed and time stamped in the signatures section. You can add or delete signatures by pressing the + or - buttons in the bottom left of the window.
Insert your signature into a PDF document
Once you've created and saved your signature, open up the document you wish to sign using the Preview app. Click on the annotate button which looks like a pencil, and then select the signatures button, which looks like an underlined capital S. Select your saved signature and 'draw' it into place by holding down the left mouse button and dragging to size.
I don't have a MacBook with an iSight or FaceTime camera, can I still do this?
Yes, but you will need to purchase a separate USB camera.
Are there other ways of doing this?
Yes, but it's a little more time consuming. You need to scan or take a photo of your signature and export it as a JPG file, which you will need to take off your camera or scanner. You would also need to edit the colours and contrast of the JPG to make it match the document colour, crop/resize and insert.