Historical Rules · 13 July 2013
Rule 107.9
Official source text from the 13 July 2013 Rules release
A tombstone icon appears to the left of the name of many _Odyssey_(TM) block cards with abilities that are relevant in a player's graveyard. The purpose of the icon is to make those cards stand out when they're in a graveyard. This icon has no effect on game play.