Office 365 (Outlook on the Web) - Email Signature
Follow these steps to create a signature that is automatically added to every new email.
1. From the Outlook app, click the gear icon in the upper-right corner of the screen and select Options from the menu.
2. Click Email signature in the Options menu on the left-hand side of the screen.
3. Type and format your signature text in the email signature text box.
4. Check the Automatically include my signature on new messages I compose box.
5. Click the Save button.
NOTE: Your signature will now be included at the bottom of every new message you compose.