Source: http://lifehacker.com/5976527/hellosign-digitally-signs-documents-right-from-gmail
Chrome: Technology has somehow made signing paperwork more annoying than it used to be. Now you have to print something out, sign it, and scan it back in if you want to email it. HelloSign adds electronic signatures to Gmail, so you can sign a document without even leaving your inbox.
HelloSign is one of the simplest electronic signing apps we've seen yet, mostly because it's integrated right into Gmail. Now, if you receive an email with a PDF attached, you'll see a new option below it to sign it. Once you connect Gmail to HelloSign, you can upload a signature from an image or draw it right into the app and use that for all your future documents. Just paste in the signature, add any other necessary info, and send it right back. Check out the video above for more info, or check out the extension at the link below.
HelloSign (Free)