Did you ever think of your finger as a legal signing tool? Softsign for iPad (free for a limited time) offers a PDF annotation tool for iOS that allows you to sign legal documents via a touch screen.
Developer Tom Hodgson points out that a variety of laws implemented more than a decade ago made electronic signatures legally valid in the US, the UK, and beyond. The 2000 United States ESIGN act specified that e-signatures could be accepted as equivalent to a written signature for commercial transactions. The EU has the 1999/93/EC Directive on Electronic Signatures, and in the UK there is the Electronic Communications Act 2000.