Outlook: add a new automatic signature

Open a new email message
Draft -> edit signature -> + -> type your signature text
Choose your default when sending new or replying messages

You can even add pictures in your signature by clicking the image icon.

More details: https://support.office.com/en-us/article/create-and-add-a-signature-to-messages-8ee5d4f4-68fd-464a-a1c1-0e1c80bb27f2