Try the following function:

Function HeaderExists(WhichForm As Form) As Boolean
On Error Resume Next

 HeaderExists = WhichForm.Section(acHeader).Visible
 If Err.Number = 2462 Then
   Err.Clear
 Else
   Err.Raise Err.Number, "HeaderExists", Err.Description
 End If

End Function

Inside a form, you'd call this as

 If HeaderExists(Me) Then
   MsgBox "This form has a visible header"
 Else
   MsgBox "This form does not have a visible header"
 End If

From a module, you can use HeaderExists(Forms!NameOfForm)

The form must be open for the function to work.

Using VBA function - the following code is not fully tested, but it should
give you the idea.

Public Function HasHeader(frmAny As Form) As Boolean
Dim TfAny As Boolean

  On Error GoTo HasHeader_Error
  TfAny = frmAny.Section(acHeader).Visible
  HasHeader = True

  Exit Function

HasHeader_Error:
  HasHeader = False 'Error 2462
End Function