You can use a Constant for stuff like that, since it is configured per environment.
E.g. use the Constant in a datasource microflow in your layout to show a special text.
There are a couple of widgets on the appstore that could help your users:
https://appstore.home.mendix.com/link/app/425//Environment-Badges
or
https://appstore.home.mendix.com/link/app/1834/Magnus-Green-B.V./Environment-Indicator-Widget
They may need to be updated by the owners if they don't work in your version of Mendix.
Regards
Simon