Which of the following indicates significant weather present in a METAR report?

The indication of significant weather in a METAR report is represented by "TS," which stands for thunderstorms. This abbreviation signals that thunderstorms are occurring, which can have various impacts on aviation, including turbulence, lightning, and heavy precipitation. Such weather phenomena are critical for pilots and air traffic controllers, as they require heightened awareness and preparation for the conditions associated with thunderstorms.

In contrast, the other choices represent different weather conditions that are not necessarily indicative of significant weather. "SCT" refers to scattered clouds, meaning there are patches of clouds but not enough to be considered a significant weather event. "CLR" indicates clear skies, which typically signify good weather conditions. "FEW" denotes a few clouds, which, like scattered clouds, does not suggest significant weather. Therefore, "TS" is the clear marker for notable weather that necessitates careful consideration in aviation contexts.