When indicating a course using the International Code of Signals, what should be specified?

When indicating a course using the International Code of Signals, it is important to specify a true course unless indicated otherwise in the message. This is because a true course provides a standardized reference that can be universally understood by all navigators, regardless of their own magnetic variations or local orientation. True courses are fixed relative to geographic North and are not influenced by the magnetic declination that varies depending on the geographical location.

Using a true course helps eliminate confusion, ensuring that signal interpreters can accurately understand the direction being communicated. Without this specification, interpretations could lead to miscommunications, especially in situations where navigational safety is paramount.

The other choices do not support the clarity needed for safe navigation and effective communication. For example, indicating a magnetic course may not align with the true North reference that others are using, while indicating a relative course could be ambiguous depending on the observer's current position and heading. The suggestion to only indicate the course when necessary undermines the importance of clear communication in maritime operations, where each detail can significantly impact safety and efficiency.