I've done some testing and i found that Linking your PSN-ID to the site really isn't very hard. all you have to do is CLICK HERE

The PlayStation Underground is the community of PlayStation fans you join by creating an account on PlayStation.com or by registering a PlayStation product. As an Underground member, you can participate in community forums and manage your account on PlayStation.com.
Underground members are also kept “in the know” about new games, hardware, events and more—so you can maximize your PlayStation experience.

Linking your IDs is a new feature on PlayStation.com that allows you to make the connection between your Underground ID on PlayStation.com, your PLAYSTATION Network ID and PS3ADDICTS accounts.

So, for example, the people you play with online (using your PSN ID) will be able to read the forum posts you’ve made on PS3ADDICTS (using your current username) and see that you are the same person. Once you’re linked up you’ll also receive a PSN ID graphic including your Avatar and “About Me” Message that has been made portable for the Web.

go into your profile and paste it as your Signature

Having an ID that you can post on your favorite social networking sites and gaming communities allows you to amp up your visibility throughout the PlayStation universe. You can use your beloved (or feared) PSN ID wherever you go on the web and everyone will know you by your PSN ID.

CLICK HERE for more information if you want it