It looks like it could be what xur uses to get to the tower, since there is a "9" on the top of the symbol. It could work like instant transmission (I just randomly thought about dragonball), where you need a reference point to use to teleport to. (To get from point x to point y in an instant, you'd have to know where both the starting point and the ending point is first.) Also, don't ask how I got here. I don't know either.