Here is smll application SISContents which allows you to unpack, edit and sign Symbian 9.x SIS packages ( Nokia S60 3rd Edition and Sony Ericsson UIQ 3.x platforms are supported).
You may some time need to Unpack SIS file or Edit SIS to see certificates against which it was signed as well as to view the PKG script that describes the on-device installation process. Normally any application developed for symbian OS need to signed with but lots of mobile application available on internet are in unsigned form.hence you need to manually sign. SISX files are Symbian OS Installer Files which lets you to install any application on your symbian OS based mobile phones.
