func (sys *NotificationSys) SignalService(sig serviceSignal) []NotificationPeerErr {
	ng := WithNPeers(len(sys.peerClients))
	for idx, client := range sys.peerClients {
		if client == nil {
			continue
		}
		client := client
		ng.Go(GlobalContext, func() error {
			// force == true preserves the current behavior
			return client.SignalService(sig, "", false)
		}, idx, *client.host)
	}
	return ng.Wait()