The rules are set down to prevent users from linking to other commercial sites or cross-promoting other vehiclePC sites in their signature lines. Linking to your own project site or personal website is acceptable. Linking to Digital-car.co.uk is not.
One member (or perhpas a group) is protesting this by requesting that people use a redirector rather than google to get here to prevent adding to Google's page rankings for mp3car.com. Frankly, I don't think that wil make any difference whatsoever, but let them have their protest.