I always assumed iG means internet Gangsters. Anytime the i is lowercase it generally stands for internet. Like iCarly.
If my memory serves correct, it came from an old ass mobile game called “iGangster” as the founders of iG originally came from that game to KaW. Internet Gangsters was the inspiration to the iGangster game though, as this was the earliest days of the Apple App Store and mobile games. A couple articles still exist on iGangster, but nothing of importance.