What are the three primary telemetry signals in observability?

Why this is the answer

Metrics, logs and traces are the three signals every observability stack is built on, and the three OpenTelemetry stabilised first. Continuous profiling is a genuine fourth signal (OTel is adding it) but does not displace traces; a dashboard consumes signals rather than being one; and counters, gauges and histograms are instrument types within the metrics signal alone.