When you create a case, or set up a template, you can choose to activate an automatic reminder to be sent. Go to Settings>Automatic reminder. You can configure the amount of days before the reminder will be sent to any parties who have yet not signed.
To send a manual reminder, you need to open the case and go to Send Reminder at the bottom right of the page. The reminder will only be sent to the person/persons who have not yet signed.
In the Case Archive you have full overview of all your cases. To see which cases awaits signature, filter them out by choosing "Sent" in the drop-down menu. The orange cases are sent, but not signed.