Mark of Sakiko is a uncommon Enchantment — Aura card from Betrayers of Kamigawa (BOK), collector number 135. Current market price: $2.91 (foil $20.60), TCGplayer market prices via Scryfall.
Enchant creature Enchanted creature has "Whenever this creature deals combat damage to a player, add that much {G}. Until end of turn, you don't lose this mana as steps and phases end."