The Movies Are Rated R, but Not on the Billboards - New York Times

Movie ads are supposed to reveal the movie's rating. But as this article shows, many billboards have "not yet rated" designations. The same artwork is not just on billboards meant to be glimpsed while traveling but also on posters on buses and subways, so the claim that it isn't important whether the rating information is there or not is as specious as the claim that they don't intentionally delay submitting the movie for review so they can leave the rating information ambiguous for as long as possible.