Thanks to my co-worker, Barb, for pointing this out to me.
The Sametime Proxy server ships with an SSL certificate to allow for push notifications to occur securely for the Sametime Mobile Chat client for Apple iOS via the Apple Push Notification Service (APNS). The current certificate expires 9 June 2015.
Before that date, Sametime administrators should download and apply an updated certificate to continue expected functionality for users.
If you haven’t updated your SSL certificate, time is running out.