I am using the following rest url to trigger boundary signal event in my application. This rest url always returning Success:true in json response though there are no boundary signal events attached to some of the human activities.
Using /process-instance/{processInstanceId}/event/{signalName}, can signal an activity specific to an activity and also just process instance. /runtime/signals signals irrespective of process instance. But none of them reporting error if signaled on activity which has not boundary signal event attached
It would give you an exception, if an exception happened.
But BPMN 2.0 wise, it doesn't matter or not if a signal that is fired is listened too or not. A signal is a broadcast, you don't care who is listening.