One of the K/1 classes made informative signs which they helpfully hung around the school.
Say sorry when you bump someone because someone might be hurt.
People are talking while going past the office.
Stop. Don't talk while Patricia is working. Shhhh. Be quiet.
[the post-it note says]
Or else she will be distracted.
This is my favorite, both for the message and the illustration:
Do not sing "Let it Go" in the classroom or else people might get annoyed!