AWS WAF now lets you generate labels and customize your WAF rules based on those labels. With this feature, you can configure WAF to add descriptive labels to web requests when a WAF rule matches the request, regardless of the action associated with the rule. You can also check for the presence of those labels in subsequent WAF rules and combine with other WAF rules to take action on web requests that include the label. Creating a label also generates a corresponding CloudWatch metric and adds the label to your WAF logs for improved visibility.
Source:: Amazon AWS