S60 3rd Edition introduced mandatory signing of applications. This means that the application does not install if it has not been signed. Generally speaking there are two types of signing:
Signing with any private key to achieve uniqueness and to confirm the integrity of the sis file. The makekeys application can be used to create the needed key and signsis to sign the application. Both applications are delivered with the SDK.
Signing with a specific private key to achieve certification — signing the application so that a trusted root certificate on a device trusts the signature on the application installation package.
The first case has to be done by the developer during the development process in order for the application to install to the device. The latter can be done through Symbian Signed program and the capabilities can be granted through it.
Note: the Symbian Signing process is described on the Symbian Signed Web site.