Does your application use a single layout for all the pages? (excluding popups ofcourse)
If yes, then you can add this to your page layout, so you don’t have to add it every page. Even if you have 3-4 different layouts used, adding it there still sounds a better option than adding it to every page.
Although answered, here is the marketplace-module that does this for you: Environment variables. Either with colors, or with a label at the top or side.