To correct some trademark misconceptions in here, just because a trademark registration is abandoned, does not mean that the trademark rights are available, the owner could still be using the mark for the described goods or services and still retain common law rights.
Also, a trademark registration is directed to described goods or services and even common law trademarks are generally for goods and services for which the mark was used (and protect against confusingly similar usages), so even if GYGAX was registered or there were just common law rights to such mark for RPGs and board games, that likely wouldn't stop GYGAX friend chicken chains or tire shops.