What does SIS slang mean?

I'm curious, could you help me understand what the acronym "SIS" stands for in the realm of slang? I've come across it in various conversations and contexts but haven't been able to pin down a definitive meaning. Is it related to a specific subculture or community? Perhaps it's a recent trend? Clarifying this acronym would greatly assist me in comprehending the conversations and cultural nuances surrounding it.