Well, nothing prevents from putting a comment on the movie page (like what Steve did on that page that you linked).

About an icon, I do not really see why, but I could add that, yes, or just show the number of cars in the movie near the title in the search result list.

About appropriate steps, as a majority did not want to list such movies I could not do anything else than deleting the two "movies without cars" that I listed, and not do anything more