Refer to figures.
Rotor brake is normally a disk brake made from steel or carbon fibre often located:

• Between the engine and main rotor gearbox, on the short shaft;
• Immediately behind the main gearbox on the intermediate drive shaft; or
• On the side of the main gearbox, with a disk around the main or tail rotor drive shaft that is gripped with brake pads operated by a lever in the cockpit.

A typical rotor brake system has its own accumulator, relief valve, pressure reducer, and shuttle valve.

As for the actuating mechanism it can be either:

• By Pull cable;
• Electrical or
• Hydraulic.

Most helicopters use a rotor brake to:

• stop the rotors quickly after shutting down the engine(s), for safety and convenience;
• stop the rotors being turned by the wind when the machine is parked and
• help with main rotor engagement and disengagement in high wind conditions in order to prevent blade sailing.

Regarding the cockpit indication will vary from a simple rotor brake "ON" light, to an indication "OFF/ON/INHIBIT" depending on the complexity of the system.

In addition, some helicopters have interlocks so that the rotor brake cannot be applied in the air.

Finally, the rotor brake SHOULD NOT be applied at a higher rotor speed than the aircraft manual states, as this can cause excessive wear or overheating of the rotor brake, possibly leading to a fire.

Therefore, the rotor brake will get too hot in case engaging the rotor brake above the maximum rotor RPM permitted.