What does the dollar sign ($) indicate on a METAR?

The dollar sign ($) in a METAR report is an indication that there is something noteworthy about the observation. Specifically, it signifies that there is a situation that deviates from the standard reporting format, typically meaning that there may be missing or incomplete data that the pilot or meteorologist should be aware of. This symbol serves as a warning or alert to users that attention is needed, particularly in situations where critical information may not be fully represented. Understanding this notation is essential for interpreting METAR reports accurately, especially in aviation, where safety and well-informed decision-making are paramount.