SIS and SISX are both installers of S60V3, the former is unsigned, and the latter is signed. Free signing requires importing a certificate and a key, otherwise it cannot be signed. (There are two ways to sign, one is above, and the other is almost to add an X to the suffix of the source file. If you don't believe me, you can try to sign the signature file with free signature, and the format will become SISXX. ) It is recommended to sign on the computer or directly crack the mobile phone, and there is no need to sign again.

The Smartphone Players Alliance answers for you. Hope to adopt.