Place the following simple rule in any folder:
 
++:L:
A=get_folder_value("_Notes_Check",item_id)
if A=="1" then msgbox("Works") end
 
If I manually put a checkmark in the _Notes_Check column, the rule is triggered and I get the message box with the message "Works".
 
If I add a note to an item using the external NoteEdit program, a checkmark is also added
to the _Notes_Check folder (by NoteEdit). However, in this case, the rule is not triggered and I do not get the message box.