Static message for one group of users?

Let's say I have a "bad users"group on my server.
I still let them join it, but they don't have permissions to build. Only to walk around and observer. Not even chat.

So is there a way to get them a constant message, freezed in the chat, or somewhere on the screen saying some custom text like "You have been a bad boy, noe you can't play on this server!", for example.

Is there a plugin like this or something?