You could use conditional formatting to flag the cell to make it noticeable,
but no worksheet function is going to prevent the save regardless of whether
the cell is properly filled or not. That's going to take a little VBA code
in the Workbook's _BeforeSave event. It will look something like this
(change sheet name and cell address as required)

Private Sub Workbook_BeforeSave(ByVal SaveAsUI As Boolean, _
Cancel As Boolean)
If Worksheets("worksheetWithCheckCell"). _
Range("cellAddressToCheck") Then
MsgBox "You must make entry here!", vbOKOnly, "Cannot Save"
Worksheets("worksheetWithCheckCell").Select
Range("cellAddressToCheck").Select
Cancel = True
End If
End Sub




"VHG" wrote:

Shared spreadsheet - When data is changed, can each cell have a identifier
requirement flag/alert (to who made the change, for example) in order for the
changes to be saved? No I.D., no saved changes.