This is the outcast symbol from "Fallout 3". The outcasts are a group of brotherhood of steel members that were cast out of the brotherhood for not following orders. Now they wander the wastelands of D.C. doing what the original brotherhood in California was supposed to do which was finding old peices of technology and weaponry that was used before the bombs fell in 2077. The technology they were looking for ranged from power armor suits, to weapons that were never used. The outcasts dont regret leaving the brotherhood and they never will.