Here's some ideas:
* Put a "hueoverride" on yourself, that way you will know you are on the dev one.
* You can also see the server name on the top left, the title of the window shows that information - just put "dev" on your server name in the configuration.
* You could also send a global broadcast that it's a dev server (might get annoying).
* If you want a gump to show up, you will have to hook a couple things (login / resurrect / etc), but keep in mind that gumps can be invasive and annoying.