Here’s how:

Click Options in the upper-right corner of your Mail page and select More Options.

From the list on the left, click Signature.

You can select Show a signature on all outgoing messages to enable the signature. Select Do not use a signature if you want to turn your signature off – or you can simply delete it manually from emails in which you’d rather not show it.

On the far right of the message window, above the text area, click either Plain Text or Rich Text. Plain Text is just the letters. In Rich Text, you can work with color, font, size and style choices that you select from the toolbar.

Note: For a Rich Text signature to appear in Rich Text, you must compose your email in Rich Text. Make that selection by clicking the Rich Text link in the Compose window, to the right of the Subject box.

Next, add or change your signature by typing in the text area.

At the top of the page, click Save Changes.

Your signature will now appear at the bottom of any message you compose.

Read more:
Add a link to your portfolio in your email signature