A few years ago, our school implemented "voice levels" as a way to help at assemblies, in hallways, and within our classrooms. This has really helped with consistency across the grade levels and made the first few weeks of school even easier when introducing these concepts.
In our school, if a teacher needs to get students' attention, he/she will hold up our hand in the shape of a zero. If kids are working in small groups and are getting a little noisy, I would hold up two fingers to remind them it was "Voice Level 2". When we create presentation rubrics, we always include "Voice Level 3" as an area to focus on. In the beginning of the year, when we are making our Daily 5 Anchor Charts around expectations, Voice Levels 0, 1, and 2 always make an appearance.
I have loved thinking of Voice Level 1 (whisper) as "Spy Talk"! In the past, I have used the fingers-on-the-voicebox trick~ if it vibrates, it's not Voice Level 1~ but the idea of talking like a spy is soooooo much more fun!
This year, I ask my Teacher's Assistant to help be my Voice Level Monitor. If they feel it is getting too noisy, they will assist me in showing the appropriate voice level with our finger(s).
Here is the file for the poster (I recently changed over my font, so it looks slightly different).
**UPDATE 12/13/13: If you like this idea, you will love my new Voice Levels Management Pack available on TpT! Be sure to download the Preview to see everything that's included and read my updated post HERE for more info!