You can automatically have your MIDlet suite signed during the packing process. Signing a MIDlet suite allows it to operate in the "trusted third party" protection domain instead of the "untrusted" protection domain. This can be significant if your MIDlet intends to access protected features.
To have your MIDlet suite signed as part of packaging, check the Sign project box on the Project Properties page. You will need to provide the location of your keystore file, the alias of the key within that keystore file, and, optionally, the password for the keystore and key.