I've read the camunda doc, but I don't find anything about it.
I know it doesn't make sense throw something that nobody will catch, but is it possible?
https://docs.camunda.org/manual/7.7/reference/bpmn20/events/signal-events/
Yes this is possible. You can model a throwing signal event when there are no receivers. The event will simply throw the signal and continue the normal flow (without anyone ever using the event).
In contrary to that, the catching signal events can not be used without a throwing signal event. If you use a catching signal event without a throwing signal event the process will stop at this event and will never be able to continue.