What sign should be placed on defective tools or equipment to prevent others from trying to operate them?

The sign that should be placed on defective tools or equipment to prevent others from trying to operate them is "Out of order." This phrase clearly communicates that the tool or equipment is non-operational and should not be used until it has been repaired. The use of this term is widely recognized in various settings, making it instantly understandable for anyone who encounters it. By labeling the equipment as 'out of order,' you effectively inform all potential users that the tool is not safe or functional, thus reducing the risk of accidents or injuries that could arise from attempting to use broken or malfunctioning equipment. This labeling practice is vital in maintaining safety and ensuring that only fully operational tools are utilized in the shop environment.