I've seen some headsets you can buy in-world for the purpose of letting people know you're on the voice first look, but honestly, that's not nearly as gaudy as we've come to expect from Second Life, so I made a bullhorn.
And I'm giving it away free. Not because I'm a nice person, but because I want you to check out my store, think nice thoughts about me, tell your buddies, and I like seeing people wearing my stuff.
It's got a pose built in. If it doesn't work when you wear it, just reattach.
Only at the Unpop Main Store
http://slurl.com/secondlife/MO%20Island/15/232/353
P.S. It won't be free indefinitely, so pick yours up now while it is.