Which of the following indicates that a rocket has been successfully prepared for launch?

The indication that a rocket has been successfully prepared for launch is when the firing circuits are armed. Arming the firing circuits is a critical step in the launch preparation process, as it signifies that the rocket's ignition system is ready to initiate the launch sequence. This step ensures that all safety protocols have been followed and that the rocket can be safely and effectively launched when the command is given.

Painting the rocket can serve an aesthetic purpose or be necessary for identification; however, it does not directly relate to the readiness of the rocket for launch. Not checking the ignition system would be a significant oversight, as this could lead to launch failure or dangerous situations. Ensuring that the launch area is clear of spectators is a vital safety measure but is more about ensuring a safe environment rather than directly indicating that the rocket is ready for launch. Therefore, arming the firing circuits is the most direct and critical indicator of successful launch preparation.