You can check the site's certificate by clicking on the slider icon next to the site's URL.
You can see the validity date and the authority that issued/verified the certificate. You can also view other details.
Signed email with certificate
The fact that an email is signed is indicated by a ribbon icon next to the sender's name (or similar indication, on the email client).
In Outlook (classic), you can verify the certificate of the user who sent you a signed message by clicking the ribbon icon next to the subject, sender, and delivery time information. This icon may be missing in the web version and other versions of Outlook.