Metric alerts in Azure Monitor provide a way to get notified when one of your metrics cross a threshold. Metric alerts work on a range of multi-dimensional platform metrics, custom metrics, Application Insights standard and custom metrics.
Note: Signals are emitted by the target resource and can be of several types. Metric, Activity log, Application Insights, and Log.
Reference:
https://docs.microsoft.com/en-us/azure/azure-monitor/platform/alerts-metric