Here are posters which are simple enough for any age group.
Four levels, from Silent to Sharing. Can be combined into one large poster or cut apart to create four small posters.
(I have added two more pages -- for a total of four -- with the same posters, but using small frames.)
I cut these apart with a curved edge then layered on colored paper. Alternatively, you could use them as is, or trim the sides only and layer to make one larger poster.
I also use a frog-shaped magnet clip to indicate the expected current noise level. I can then ask, when needed, "Where is my frog?" :) Hope you find them useful!