When I was in elementary school, the principal's office faced the playground.
When snowball fights were permitted, he would put up a green flag in the window. When conditions were too icy for safe snowballing, the red flag would go up.
God, that's beautiful. I had a sixth grade teacher with a massive pingpong paddle thing named Smackswell. Any tomfoolery resulted in two hands on the front desk and a couple sharp swats. Everybody seemed to enjoy the spectacle. This was something like 1976. Imagine if that was done today.