Depending on the size of your classic Outlook window and whether you're composing a new email message or a reply or forward, the Message menu and the Signature button might be in two different locations.
In the E-mail account drop-down box, choose an email account to associate with the signature. You can have different signatures for each email account.You can have a signature automatically added to all new messages. Go to in the New messages drop-down box and select one of your signatures. If you don't want to automatically add a signature to new messages, choose (none). This option does not add a signature to any messages you reply to or forward.
Type a new signature to use in your email
You can create an email signature in Outlook on the web or Outlook.com that you can then add to all outgoing messages or add manually to specific ones.
Select Settings at the top of the page.
Select Account > Signatures.
Under Email signature, type your signature and use the available formatting options to change its appearance.
Select the default signature for new messages and replies.
Select Save when you're done.
If you've created a signature in Outlook on the web but didn't choose to automatically add it to all outgoing messages, you can add it later when you write an email message.
In a new message or reply, type your message.
If you created multiple signatures, choose the signature you want to use for your new message or reply.
When your email message is ready, choose Send.