To each their own, but I would never blow a whistle at a group of adults. Treat them like the adults they are, not like the children the can behave like. By treating people with respect you always walk away knowing your standards are intact.
Yes, you do have to come out of your shell in order to get attention. First and foremost, dress nicely and look like an authority figure from the get go. Saying loudly, "Ladies and Gentlemen, quiet please" has always worked for me, in companies across the country. If that doesn't work I'll clap my hands twice and repeat myself. I've never had to resort to anything beyond that.
It's human nature for a bored group of people to stand around and talk, and although it's irritating to us, I find gentle reminders to be more helpful than angry confrontations. Remember that angry confrontations come off as a power trip, and if that's how you choose to be percieved, that's certainly your choice, but I've never found it to be helpful.
We are "the iron fist in the velvet glove" . . . . .