Hang this awesome flip chart outside of your classroom and simply flip to the correct tab to make others aware of what is happening in your classroom before entering. This can be extremely helpful when unexpected behaviors are occurring that interruptions can prolong or escalate the situation.
There is also a black and white version that looks great on colored paper!
Feel free to add suggestions below of other signs you may like to see.
Fonts from: Graphics From The Pond - https://www.teacherspayteachers.com/Store/Graphics-From-The-Pond/Category/Fonts-7662
Clip Art from: MyCuteGraphics.com