Nothing as annoying as someone entering the space that your yoga class is in when you're “in the flow”.

This sign should clearly indicate to anyone to either enter quietly or not at all.

I've added the Fusion360 design for you to improve upon :-)

Can be hung with a simple wire (wire hole is 5mm) and for example this wall hook: https://makerworld.com/en/models/80117?from=search#profileId-103614