Which aspect describes the STOP signal?

The aspect that accurately describes the STOP signal is a solid red aspect without a number plate. In railroad signaling, a solid red light serves as a clear and universal indication for train crews to stop and maintain stop limits until further instructions are received. The absence of a number plate on the signal is significant, as it emphasizes that the signal is conveying a command that must be obeyed without any additional information or conditions that would typically be indicated by other signals or aspects.

Understanding this distinction helps ensure safety and compliance with operational protocols, as the red signal is a fundamental element in governing train movements and preventing accidents.