There is a fine system in place for 'obscene' or 'violent' material: the rating-system. The rating-system should however not be intrusive: a green or red star with a number should suffice. A parent can easily identify the product as 'suitable/unsuitable' for his/her child.
Once the item is bought and in possession of the buyer, no one wants to be nagged with that rating-system anymore (if the DVD cover says 'R-Rated' we certainly do not want unable to skip logos, trailers, warnings saying that the DVD has that rating: we already have the damn DVD! it's already ours! We already saw the rating on the cover and popped in the DVD anyway! We are already watching it!! Gorram!!).
We saw the rating, we or the parents chose to ignore it. That's that. period.