I hope I didn't misunderstand this... lol. In terms of signing something digitally, I don't know too much about the technical version of doing this that has been mentioned (using some software). What I do is insert my actual sig (an image i've already created by scanning) into the contract, PDF it & send to the client - then they sign, scan, & email back to me.
Another option for sticking a sig image into a PDF, is just by creating a "button" in the PDF & using your sig image as the "fill" for it. (probably a better way to explain it, but that's the short version - & you need PDF editing capability too.)
I'm interested in learning more about the digital "signing" software that has been metioned though - will look into it, thanks.