For a trader needing to refer to a car maker, or other business, in this way, the distinctions drawn in this American case are useful guidance - though not, of course, binding on English or European Community courts.
The defendant, Shokan Coachworks, had used "Shokan Audi Parts" in its email signature block - a usage which, the court thought, could create consumer confusion. The strength of the Audi trade mark was a factor in coming to this conclusion (but if the trade mark had been weak, there would have been little point in using it this way, perhaps).
As for nominative fair use, the test applied by the court (the 9th Circuit's test, preferred over that of the 3rd Circuit, if you're interested) was:
1) the product or service in question is not readily identifiable without use of the trademark;In this case, the court held that Shokan had fallen at the third hurdle and their use of the name in their signature block, and also when answering the phone using their trading name "all Audi", which was the key part of the free telephone number that Audi had previously agreed to them using.
2) only so much of the marks are used as is reasonably necessary to identify the product or service; and
3) the user does nothing that would suggest sponsorship or endorsement by the trademark holder.
here was also another interesting aspect to the claim, namely that Audi alleged infringement by using an email address that incorporated the Audi name. however, they failed to produce suitably authenticated prinouts of web pages to satisfy the court - illustrating an important point about proviving trade mark infringement on the Internet.