This feature allows admins to check the latest signature that has been applied to users from SignatureSatori. Since it's loaded in real time, they can also use it to spot any user-made changes to it.
Note: We only access the default "My signature" in Gmail. We don't see any other custom signatures that might be in their account, even if they have them set as primary. If you're not sure about how multiple signatures in Gmail function or how we work with them, please check this article.
First pick the user whose signature you want view from the list in Users & Set-up. Navigate to the three vertical dots on the very right in the corresponding row and click them.
You will see that (among other options) there's Compare preview to Gmail signature. If you click on it, a window will appear displaying the current preview for the user and the signature user has exactly at that moment in their Gmail.