An e-mail signature is a small message added automatically to the end of all of your e-mail messages. It can be as simple as a name, address or phone number, or as elaborate as a poem you have written yourself. If you use Yahoo! Mail, you can add a signature to your messages and activate it when you want to use it. All you need to do is make a few quick changes in your mail options.
Log in to your Yahoo Mail account.
Click the arrow next to "Options" in the top-right corner and select "More Options."
Click "Signature" on the left side of the screen. The signature box will open.
Type your desired signature into the box. Make sure "Show a signature on all outgoing messages" is selected and click "Save Changes" at the top of the page.
Click "Back to Mail" in the top-left corner to return to your mail.
Be careful what you use as a signature. What might sound cute to you may not be so comical to others.