Which of the following indicates calm winds in a METAR?

In a METAR report, a wind speed of 00000 knots is the standard notation used to indicate calm winds. This specifically means that there is no significant wind being detected at the reporting station. Calm winds are important for pilots and air traffic controllers as they affect takeoff, landing, and overall flight operations.

The other options may relate to wind conditions but do not explicitly indicate calmness. For instance, light winds suggest a degree of air movement but do not qualify as being completely calm. Variable winds indicate that the wind direction is changing, which implies some level of wind presence. Finally, "no report" does not provide any information about the wind conditions at all, leading to uncertainty rather than a definitive indication of calm weather. Thus, the correct answer clearly signifies a complete absence of wind, a critical factor for aviation safety and planning.