As you will notice via the screenshot above users have several other options other than simply formatting the screen, one of those options is the ability to encrypt and therefore protect your personal files. If you choose this option you will be able to choose a media card specific password or use your Blackberryd devices password, this ensures all of your files are protects in case you ever lose your memory card.
To set a randomly encrypted password simply choose Encryption Mode: Device and to set the password to be the same as your Blackberry choose Encryption Mode to Security Password. Conversely if you want to choose both options to add even more security you can choose the encryption mode: Security Password & Device.
Whichever option you choose as you can see it's an easy process.