Did I once hear from another DBA that Oracle puts a file somewhere in $ORACLE_HOME signaling the instance/database is started and the absence of the file means it's down? Or was I just dreaming?

If it was a dream, then I can check
ps -ef | grep smon

Is there any other creative ideas from the O/S showing the state of the dB? This must also work if the instance is shut.

thank you!