One of the most useful and hidden features in OS X is that you can sign documents without any other tools. In OS X 10.7, Preview gained the ability to add your signature to documents. To get started, go to the Signatures tab in Preview's preferences and then click the +. Now, sign your name in black ink on a small piece of white paper and hold it up to your Mac's webcam. Line it up and click Accept (making sure the 'Save this signature' option is checked if you want to use it in the future). Now open a document you want to sign, pop up the Edit Toolbar and click the signature icon – it looks like an S on a line next to a tiny X. Draw a box to add your signature on the form. You can scale and reposition it afterwards too.