How can I detect if the user is in Group Mode when a macro starts

I have a macro that needs to warn the user if they are in group mode before it runs its main actions. I can't find a mechanism like..
If Selection.Sheets.Count 1 or For Each aSheet In Wb.Sheets, If aSheet.Selected = True etc. etc

I have a fix that writes an unlikely entry and then looks through the sheets to see if the unlikely entry has appeared on other sheets but there must be a better way than this

Any ideas much appreciated

Rog