There is a great difference between street gangs & syndicates like the mafia or yakuza. Indeed sg 'gangsters' are more to delinquents kids rather then real gangsters. They are quite similar compare with other countries and easily mistaken as real gangsters.
Not all sg 'gangsters' are involved in secret society activites. Even if they are, they are consider in the lower rank. They may have a 'zhong', but they dun know who their real 'boss' is. (they are not suppose to know.)
Probably these 'bosses' are running the show in Geylang... those night clubs/ pubs, massage parlors, maybe few of the shops at lucky plaza.

While they are making money, do u think they want to get involve in a fight like staring incident caused by their 'gin nas'?
Sg too small already, no where to run... even to malaysia. In addition, thanks to sg gov & the police using both iron fisting & psychology warfare. Unlike local syndicate or secret societies, overseas mafia have their own illegal businesses, also have support from legal businesses, few even have links in politics.
Maybe for those groups that hang out aimlessly at certain places looking for trouble be call hooligans rather then gangters?