Microsoft made changes in Excel 2007. In Excel 2007, the file name must be .xlsm to contain macro. If it is .xlsx then it will not contain macro. This is true only on Excel 2007 – not on previous versions of Excel.
I do not know of any way to determine this without opening them, no.
Then if FreemaG is using Excel 2007, it would be fairly simple to display all spreadsheets in a folder using the ‘details’ view – which would identify the spreadsheets with macros though the file extension…..