This idea is actually a gem that one of my students thought of a few years ago!!! One of my classes' favorite YouTube videos was this one... "If You're a Boy" from Harry Kindergarten.
Well... my kids were chatty one day and I said "If you're a boy zip your lips." One of my girls said "If you're a boy, a boy, if you're a boy zip your lips!" And so a new tradition was born!
When my kids get chatty, all I do is start to sing the song!
If they're extra loud, I have them do actions that will get the other students attention (e.g. ones that make them move more or make more noise) such as: pat your legs, jump up and down or clap your hands.
If there's only one or two students chatting, I usually do more silent action, such as zip your lips, fold your hands.
I actually also use this to get my students to clean up at the end of their writing period. I break it down step by step for them (since they're kindergarten), so I'll say "If you're a boy, a boy, if you're a boy put your crayon away." Then I follow it by fold your hands, push in your chair, and walk to the carpet.
How do you get your kids to quiet down?