You must have it first. Cer and Make a key file for your serial number (you can apply on Saipan forum), and then use the "free signature" software (available on Baosoft). Or submit the serial number directly on Baosoft or 3G. It seems that you can download the software to be signed directly from the website after you finish it, but it has already been signed.

In fact, it is better to crack it, sign it once, and then be free!