Determine if Running as a Subreport

I want to hide or show a row based on whether a report is being run standalone or being run as a subreport. Is there a way to determine if a report is being run as a subreport? I know I can probably use a parameter field and pass a value when the report is being run as a sub, or NULL if standalone, but I am hoping there is an easy built-in way to determine this. TIA