Every application must be signed, but you can self-sign in some cases.
a ) for a application with basic capabilities, you can self-sign, such capabilities are : LocalServices, NetworkServices, ReadUserData, UserEnvironment and WriteUserData (and location?), webpage say that location is allowed but forum say otherwise.
This allow to use multimedia features such audio? Or for example a game?
Location is related with read the IMEI?.
b ) If you required more capabilites then you can create a imei specific in the simbiansigned webpage. Fexplorer for example ask for it.
Can you reuse old certification?.
c ) but for a commercial use you will need to run the whole certification process, can take many months and cost a lot, also can be rejected (start over the whole process, not just time lossed also money).
Also i wonder what's the point with antivirus?.