An Email Signature consists of text and/or images that are automatically added to the end of any outgoing email message.
You may choose to have many Email Signatures that serve various functions e.g. an internal company signature as opposed to a Client-based signature, and even a personal email signature if required.
Learn how to setup your Email Signatures here:
1. How to Setup an Email Signature – Outlook 2010
2. How to Setup and Manage Signatures – Apple Mail