Remove Signature From Guests for phpBB

Linking to websites with a low PR or unrelated content from your site may lower the importance of your webpage. This will remove any links or unrelated text from guests (search engine bots) to improve the quality of your site. When a user logs into your forum the signatures will be viewable again. Another minor thing this helps (for those who care about this) sometimes someone's signature would result in bad HTML for the viewtopic table when using the HTML 4.01 validator tool. Removing the signatures from guests will prevent an error from someone's signature.