Everything below that is FREE marketing space.
I add a link to Join My Mailing List.
You can also add a message, maybe a mention of a special event you have coming up, or a discount you're offering on a product or service. You can even create multiple custom signatures with different messages.
PRO TIP: If you have staff, make sure that all signatures contain the same information.
If you need help, here are a few support sites. You can also Google "create custom email signature with hyperlink Outlook 2013" (include which version you use).
Outlook support: support.office.com/en-us/article/Add-a-return-e-mail-address-link-to-a-message-aa26c703-5c94-4be8-82cd-1839f3cd8934
Gmail support: https://support.google.com/a/answer/176652?hl=en