jdrakeh said:
Your example comparing aftermarket auto air filters to RPG trademarks is not unlike comparing apples and oranges. Such a lawsuit has already been won versus Mayfair games back in the day. Using somebody else's trademark to promote your own game without their permission generally results in a judgement against the infringing party.
OK, i'm going on memory here, because i don't have good resources handy, but i know it's not that simple. For starters, there were two lawsuits. IIRC, one was settled, one was decided in court. And, again, IIRC, the one that Mayfair lost was a contract infringement--which, admittedly, was the result of the settlement of the first case. But, nonetheless, there wasn't a clear-cut "Mayfair is using TSR's trademark unfairly" court decision. Rather, that was the accusation that TSR leveled; TSR and Mayfair settled out of court, allowing Mayfair to keep using the trademark; TSR alleged that Mayfair violated the terms of that agreement and sued; the court agreed and found against Mayfair. [going on memory here, admittedly]
And, back to your fundamental point: i'm not sure the relationship was ever so clear-cut. Was Mayfair using the D&D trademark to promote it's products, or using it's products to promote the D&D trademark? Personally, i think it was both--they were giving as much as they were getting, roughly.
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And, to answer a couple other people: yeah, there are some very complicated issues of derivative content, that have only become more complicated with court decisions in the last decade or two. But that's a rather distinct issue from the use of trademarks to indicate compatibility. [And that's before we even get to ideological concerns about the growing imbalance between large media companies and the public, where IP laws are concerned.]