Most venues require a $1+M general liab. policy - it is standard practice. However, it would the the show management that would provide the proof of coverage to the show venue. The show management may require this same coverage from any exhibitor who plans on setting up an exhibit at the show.

I am not sure why a venue would require an individual show participant to have a $1M policy, unless the participant is planning on having a booth exhibiting the car. But, I believe this still falls under a general liability policy, not a $1M policy for the car.