Rare Wondrous Item (Coin), Requires Attunement

Due to an illusion cast upon it, this magical coin appears ordinary, but when examined, a DC 18 Intelligence (Investigation) check can reveal the symbol of an eye upon it, and a small crystal gem embedded into its centre. 

Unlike most other magical items, you cannot lose attunement to this item by being too far away from it, and you can attune to multiple copies of it, but each requires its own attunement slot. 

Golden Eye. While attuned to the item, you can use your action to cast the Arcane Eye spell on its location, as long as the coin is within 50 miles of you. If the coin is in a storage or container, the Arcane Eye will appear outside of it, as long as it is within 30 feet of the coin. If the eye moves further than 30 feet away from the coin, the effect of the spell ends.While attuned and holding the coin, you have darkvision out to a range of 30 feet and once per short rest, you can cast the Hunter’s Mark spell using the item with a +5 bonus on Concentration checks to maintain it.