I found it interesting that they chose "23". It's a number that has been called "mystical" in many numerological belief systems, especially recent pop-culture ones. As such, they get to tap into this vast '23' zeitgeist. People have been secretly including the number in all kinds of stuff for ages, so it's like a hundred-year unofficial ad campaign for their movie. Also, people who see it will suddenly start to notice 23 cropping up all over the place. The movie looks crap, but that bit of marketing strategy was kind of genius.