I try to be as much of an entertainer as possible when I speak. But sometimes that can get the kids a little out of control. Also at the end of class, I let them talk in line until their teacher arrives. But when it's time to get quiet, it's helpful to have a silent signal.
Sure, there are great ones out there like putting two fingers in the air to signify "peace & quiet" or "if you can hear my voice, clap 20 times (then take a bow, like they're clapping for you." But I wanted something that felt like it was made for older students, especially the ones that are To Cool for School (yes, I spelled it that way on purpose).
I call it the BOOM BOOM CLAP silent signal. I bang the wall (or a piece of equipment two times) and they clap once (it sounds like the beat to We Will Rock You). They love it. Of course, like any silent signal, it takes work and upkeep. I don't normally like to single students out, but it works well with this one. After two tries, I'll do the BOOM BOOM part, then while they clap, I say student's names who need a little extra nudge. "BOOM BOOM Dave, BOOM BOOM Claire, etc."