RIM has article on signing keys and how to obtain them here.

When you receive the signature files from RIM, place them in the bin directory for each jde for which you would like to sign.

Configure maven for signing using your key and passphrase by:

1. Editing your metovaMobilePlugin.xml
2. Changing your <mode> to release and make sure your <passphrase> is filled in

   <mode>release</mode>
   <activePlatformId>rim-4.6.0</activePlatformId>
   <stagingDir>c:/YOURBUILDDESTINATION</stagingDir>
   <platformTypes>
   	<platformType id="me">
   		<obfuscate>true</obfuscate>
   		<signing>
   			<passphrase />
   		</signing>
   	</platformType>
   	<platformType id="rim">
   		<obfuscate>true</obfuscate>
   		<signing>
   			<passphrase>YOURPASSPHRASE</passphrase>
   		</signing>
   	</platformType>
   </platformTypes>
   <platformVersions>
   

3. Executing a build as you would for development.

Your build should now be in <stagingDir>