Here ya go. This is what one prop seller prints.

Do not operate any propeller until you have thoroughly read and understood the following instructions and warnings!

A rotating propeller has the potential to be very dangerous and can cause personal injury. It is the responsibility of the user to be aware of this fact and to operate it with extreme care, common sense, and good practices. Inspect the prop before each use for any signs of damage or irregularity. Remove and replace any damaged or irregular prop. Do not attempt to repair it. Be sure that it is balanced and mounted properly. Check the prop bolts often for proper security. Do not allow a spinner to rub against the prop. Do not hand start your engine. Always remain clear of the rotating prop blades. Never reach toward a spinning prop or allow anything or anyone to come near it while in operation. Keep people behind the plane of the prop. Do not run the engine at high RPM in the proximity of personnel or property. Always operate over a firm surface. Never attempt to stop the engine by throwing any object into the propeller.

Here's your sign.