There are a LOT of reasons why you would want to have an electronic signature on-hand and ready to use... email signatures, signing documents, etc. The question isn't "Will I use an electronic signature?", but rather "What's the easiest way to create an electronic signature?"
There are really two ways to "ingest" a signature into your Mac to use. The first way is by signing a paper and either scanning it in, or using your iSight camera to capture it (more on that here). The other way is where I wanted to focus this post.
Trackpads are becoming more and more popular, even with desktop computers. I prefer a trackpad over a traditional mouse for two reasons: 1) because I like a sense of continuity when switching between my laptop and desktop and 2) it allows me to use multi-finger gestures in a way that I never could with a traditional mouse.
The trackpad is good for much more than the above arguments. For example, you can use your trackpad to create an electronic signature, which can then be used to sign PDFs, etc.
To use your trackpad to create a new signature, we first need to open Preview. With Preview open, go to Tools > Annotate > Signature > Manage Signatures. Next, we will click on the button that resembles a small signature.
At this point we will see a drop-down window that shows us what signatures (if any) we have already added. In my case, I already have one. To add a new signature, we'll click "Create Signature".
Next, we will be shown an area that looks like your trackpad. When you're ready to begin, simply click the button in the middle of the trackpad.
Once you have signed your trackpad, you'll need to press any key on your keyboard to signal to OS X that you are done signing the trackpad. Your screen should look something like this (only with your signature):
Now that you have created your signature, it's time to use it. With a PDF document open, and the annotation toolbar still active, we will click the signature button again, and choose the new signature that we just created. This will insert the signature in your document. At this point, you simply need to adjust the size and location of the signature, and you're done!