Передайте ручку вашего приложения и частичную подпись. Он вернет true, если найден.
Public Function GetHandleFromPartialCaption(ByRef lWnd As Long, ByVal sCaption As String) As Boolean
Dim lhWndP As Long
Dim sStr As String
GetHandleFromPartialCaption = False
lhWndP = FindWindow(vbNullString, vbNullString) 'PARENT WINDOW
Do While lhWndP <> 0
sStr = String(GetWindowTextLength(lhWndP) + 1, Chr$(0))
GetWindowText lhWndP, sStr, Len(sStr)
sStr = Left$(sStr, Len(sStr) - 1)
If InStr(1, sStr, sCaption) > 0 Then
GetHandleFromPartialCaption = True
lWnd = lhWndP
Exit Do
End If
lhWndP = GetWindow(lhWndP, GW_HWNDNEXT)
Loop
Функция завершения