An odd semi transparent shape that reacted to being noticed.

Outside the front of my house, my sister and I were smoking a cigarette and shortly thereafter in the corner of my eye I seen movement above the broken treeline, I asked out loud to my sister as to what that is. She seen it as well as asked the same question as it quietly drifted behind the tree line and then vanished. It was the shape of a Chevron but closed on top. It was semi transparent but in appearance however we could not tell if this was a craft or a being.