This also confused me when I first started using vROps.
Inherited with a tick = this alert is enabled via another policy that this policy is inheriting
Inherited with a circle cross = this alert is disabled via another policy that this policy is inheriting
If you want to enable or disable the alert via the current policy that you are editing (instead of relying on one of the parent policies to set it), you can change to "Local tick" (will enable it in local policy) or "Local with circle cross" (will disable it in local policy)
Let us know if you have any followup questions