Farm in Trial best practices report by SPDocKit determines whether the SharePoint farm is in trial.
Farm in Trial
This check determines whether the SharePoint farm is in trial.
If you are using the trial version of the product, you will need a valid license key to continue when the trial expires. The trial version is valid for 180 days from installation, after which your farm should be upgraded to the full version.
Your license status can be checked through Central Administration. You can license the full version by paying for a license key, then navigating to Central Administration > Upgrade and Migration > Convert Farm License Type, where you enter the key.