Autograph (US$6.95) is a signature capture application that works with your MacBook and a finger or stylus to make signing your name a snap. If you don't know if your MacBook will work with Autograph, you can download a trial copy that adds a watermark to the signature just to try it out.
To add your John Hancock to an email or document when Autograph is running (I have it set up to launch at startup), you can either select the menu bar icon or press control-option-A, and then a semi-transparent gray window appears. Using your finger or a stylus on your trackpad like a pen, you can write your name or draw a little picture. Pressing return embeds the signature or sketch into your document.
Autograph works great! I was able to use it in Mail, Word, Keynote, and Pages, and I'm assuming that it will work fine in any Mac application that lets you paste in a graphic. I know I'll be using this handy little program to add a personal touch to my documents. The short silent video below demonstrates Autograph in action.