This is, what I presume, a UI generated notification that pops up when your traitor buddies purchase T items. It will work similar to how the chat notification popped up whenever someone bought a Jihad on SGM servers.
Be honest here, when was the last time you had teammates that gave good callouts if any? At least with this you know if a harpoon could potentially come flying at you. Could also help dets a lot by not having to waste credits buying a health station when ones already bought.-1. I think this kind of ruins the "teamplay" aspect of the game, where you need good communication to know what this addon lets you know for free.