What’s a cult? Basically it is a parasite structure that lures its members in belief they do something while all they do is wasting their own life and savings.
The main question is how to find a difference between cult and valid non-profitable urban games. Mind control technique used by cults give a kind of answer.
The typical writings on the wall are:
Other pages of CIC (Cult Information Centre) site contain some interesting data too, but IMHO its FAQ section is the best.