The "My signature" pane
“My signature” is a button on the Outlook compose ribbon. It opens a small pane that applies your signature on demand.
Most of the time you will never need it. It exists for the times when the automatic path cannot do its job.
What it does
Section titled “What it does”It applies your signature immediately and shows you a preview of what was applied.
If it could not, it says why, in language you can act on rather than an error code.
It offers a download of your signature as a self-contained file.
What it tells you when something is wrong
Section titled “What it tells you when something is wrong”The pane distinguishes between problems worth retrying and problems that retrying cannot fix.
Where a retry might work, the Apply and Download buttons stay where they are and the explanation sits above them. A failed sign-in, a connection that dropped, or Outlook declining the signature all fall into this group.
Where nothing can be applied to this mailbox at all, the buttons are removed and only the explanation remains. That covers a mailbox with no signature configured, an organisation that has not finished setting Sigil up, a subscription that is not active, and a version of Outlook too old to support the add-in. Offering a button that could only fail would waste your time and tell you nothing.
Each of these names who can fix it, which is usually your IT team rather than you.
Opening the pane does not front an error on its own. If something is merely transient, you find out when you press a button rather than the moment the pane loads.
Why it exists
Section titled “Why it exists”The automatic path runs in a part of Outlook with no user interface. It can sign you in silently, but it cannot show you a sign-in prompt.
So on your very first message, or after your session expires, or after a multi-factor prompt, the automatic path may have no way to authenticate you. When that happens it stops quietly rather than interrupting you, because an error bar on every message you write would be worse than a missing signature.
The pane can show a sign-in prompt. That is what makes it the fix: opening it once completes the sign-in that the automatic path could not, and from then on the automatic path works.
Download my signature
Section titled “Download my signature”The download saves your signature as a standalone HTML file with the images embedded in it, so it works anywhere without needing anything else alongside it.
It is useful for pasting your signature into another system, keeping a personal copy, or sending somebody exactly what your signature looks like.
Where it is not available
Section titled “Where it is not available”Outlook for iOS and Android have no “My signature” button. Outlook mobile activates add-ins in read mode only, and a compose pane is not one of the exceptions.
Your signature is still applied automatically on mobile. What you lose is the manual fallback.
If your signature is not working on your phone, open the pane once on a computer. The sign-in is tied to you rather than to a device, so fixing it once fixes both.
If the pane itself does not appear
Section titled “If the pane itself does not appear”The button appears on the compose ribbon once the add-in has been deployed to you. If it is not there, the add-in has not reached your mailbox yet.
Deployment propagates over 6 to 72 hours, so if your organisation rolled it out in the last few days, waiting is the answer. Otherwise ask your IT team, who can check whether you are in scope for the deployment.