The biggest I've used is a discrete naming-scheme where prod-systems are named obviously different than test/dev instances. This makes the "Username@Hostname: " style prompt visibly different. And by obvious I mean more than just different words, different formats too:
example: PRD-WEB001 vs DEVEL-BOB-WEB001
This has several things going for it:
- The extra hypenated block makes it a set-of-three instead of a set-of-two.
- The first of the set is a different length.
- The overall length of names is markedly different, which makes the command-line spacing different relative to each other and other text in the window.
And best of all, it doesn't require special terminal-configs for production just to avoid Oops errors.
In my experience, you want something that is a constant reminder of where you are. Login-methods like riddles are good for about 10 seconds, until you forget which window is which. All it takes is to do an
ls in the wrong directory to scroll the ominous login-banner out of view, bury the terminal window under a browser window while googling something, alt-tab back to the wrong window and mayhem ensues. Best to have some constant visual cue like a significantly different command-prompt.