The break was short-lived! Without further ado, first tip of 2017.
If you navigate to your Dynamics 365 Administration Center and display all solutions installed in your organization, you will be able to see the version of the solution(s) installed but not the version of the portal code itself.
Just add /_services/about to your portal url:
In addition to the version, you’ll see a guid that identifies the portal product id within your O365 tenant. Both pieces of information would come handy when raising support requests for any issues related to your Dynamics 365 Portal.