Electronic signatures or eSigs are graphic images that can be made to look like a business card, or whatever you want it to look like. This graphic is appended by your email program to be appended to each email that you send or reply to.
The eSig can be configured to go to any web site when someone clicks on it. So it acts like a advertising sign pointing people to your business or home page.
I initially created these for my wife's Tupperware business. It has been a big help in advertising the monthly specials that Tupperware features in her emails.