They already sign such a document. It's called the cruise contract. I suppose you are suggesting that it be laid out in large block letter primary style so that even the most dense and ill informed passenger can figure it out. Unfortunately that is not going to happen. The basic result would be that the industry would needlessly scare off thousands of potential customers, that are all to willing to entertain fantasies (or nightmares) that they are boarding the Poseidon or the Titanic. The vast majority of cruises are completed with out a hitch, either weather related or mechanical related. Why needlessly remind peope that they could end up floating around in a lifeboat in the middle of the ocean when the chances of that happening are probably less then the passenger being struck by lightening in their own home town?