Which of the following is NOT a safety device found on cranes?

Speedometers are not considered a safety device found on cranes. They are generally used to measure the speed of the crane's movement but do not directly contribute to the safety mechanisms implemented on a crane. In contrast, the other options listed serve crucial safety functions.

An anti-two-blocking device is designed to prevent the load lines from being over-wound on the hoist, which can cause significant damage and safety risks. Overload sensors monitor the weight being lifted, providing warnings or automatic shutdown to prevent overloading, which is a critical safety concern. Limit switches are employed to control the movement limits of the crane, ensuring that it does not exceed safe operational boundaries. Each of these devices plays a vital role in enhancing the overall safety when operating cranes, making speedometers not applicable in this specific context.