Maybe the admin in charge of designs just happened to miss the vibrating underwear when they were doing the review. There must be more than 50 different designs pouring in a week in this game with how much you can customize.
I don't think I've ever encountered this before. Maybe a symbol or shorthand lettering on the first page to represent Trigger warning sounds like a good way to do it. Then again, does Lusternia's lore have trigger warning as part of their IC culture…