Historical Rules · 8 April 2016
Rule 711.1b
Official source text from the 8 April 2016 Rules release
A double-faced card’s back face is marked by a back-face symbol in its upper left corner. On cards in the Innistrad block and Shadows over Innistrad set, the back-face symbol is a crescent moon. On Magic Origins double-faced cards, the back-face symbol is a full Planeswalker icon.