This WFMW tip is actually borrowed from our local elementary school. I was thinking about it while at work yesterday when some of the students were getting too loud and rambunctious. It would work at home as well. I have even thought of using it for babysitting kids, but they are very well-behaved and I haven't had to resort to it yet.
The school uses a stoplight format- green, yellow, red- to denote behavior in the classrooms and at the lunch tables.
For example, each student has a clothespin with their name on it. The clothespin gets clipped to a circle of cardboard that has sections painted green, yellow and red. If the student has to be warned about behavior, their clip gets moved to yellow. If the behavior problem continues, their clip gets moved to red and they are sent to the office.
The system works the same at the lunch table. There are plastic cups (the disposable SOLO brand cups) stacked (top to bottom) green, yellow, red on the end of each table. If the students get too loud or are misbehaving, the lunch monitor moves the green cup to the bottom so the yellow cup is on top. If a table continues and gets moved to red, the students will not be allowed to talk for the rest of the lunch period. Since they are always seated according to classroom, the class with the best behavior at lunch gets "table of the day" and gets recognized on the next morning's announcements.
This is a great way to encourage positive behavior. It puts the kids on alert if they have been warned and is a visual reminder that they, and all of their peers, can see clearly.