Fly app’s name is a NATS subject (ref) that you can choose to not subscribe to: Ship logs from multiple apps - #5 by dusty
According to the github readme, the subject is of form logs.<app_name>.<region>.<instance_id>.
Another (obvious) way is to filter out logs after it is sent to the sink (like honey-comb, logdna, papertrail etc): fly-log-shipper: staging vs. prod & then hiding individual server logs - #2 by mhostetler