rebmuda triangle bag?

I found a bag in a fridge in one of the houses next to the neighbors that had the text "rebmuda" and a triangle with a question mark in the middle. it was on the third floor and required me to use the grappling hook to get to it but i assume you could also use a fire extinguisher. i cant seem to find a use for it but it seems like a key object for something given its name and how it was hidden. i have no idea what its for