Differentiating Test site from Development Site (ASP.NET)

We have a couple of ASP.NET applications running here at work and our users get the test site confused with the production site. What is the best way to help the users know they are at the test site. Is there a best practice for how this can be accomplished? Maybe have a custom control or something on the screen 开发者_如何学Godisplay "TEST SITE"? Thanks

I use a different style sheet, that changes background colors and other elements, to make it immediately obvious which site I am using.