Based on some of their featured comics...
Mentioning prostitution is fine (a number of their comics have this)
Blood is fine, but it depends. On their Korean site, one comic that requires age verification has bloody scenes... nothing particularly graphic in terms of visuals, but the story is very realistic, dark (based on real life, modern day serial killers) and devoid of lighter elements. The combination of the visuals and the tone of the story is probably what required the age verification. Again, that was on their Korean site, but it may help provide a hint as to how things will be handled on their English site.
Graphic depictions of penetrating injuries (e.g. a spear going through a body), cutting off limbs/ fingers/ heads/ etc, evisceration, etc. are to be censored. See Hive, one of their featured comics. The latest episode at the time of writing has penetrating injury shots toward the end, and you can see how it's censored with a white dot.