According to this help page, you can get someone's attention by starting a message with @. But I don't see what it does. What I want is similar to IRC - normal messages don't make a sound effect, but messages with someone's name do. Is that possible with Campfire?
There's John Wood's Campfire plugin, which can do what you wish:
You can also play sounds on demand in Campfire by typing "/play bueller" or another one of the sounds listed here: