Runewarding Ring

Ring, rare (requires attunement)
  This stone ring is marked with the brand of a mysterious cult dedicated to the worship of infection and decay. Fashioned of cracked, grey stone, red, glowing veins furrow its craggy surface.
  This item has 3 charges. To regain a charge, you must slice open your hand, taking 1d4 slashing damage that bypasses resistances and immunities and expending a hit die, and smear the fresh blood across the symbol. In response, the glowing veins flair a bright, molten red.
  While wearing this ring, you can use an action to expend 1 charge and press the ring against any non-magical surface or object, marking it with a glowing red symbol visible only to you. The next creature that moves within 5 f eet of the symbol must make a DC 15 Constitution saving throw, taking 3d10 necrotic damage on a failed save, or half as much damage on a successful one. After 8 hours, or if you use the ring to create a second mark before the first one is triggered, the first one fades without incident.
  Uncommon variant: Decrease the saving throw’s DC to 13, and the damage to 3d6.
  Very rare variant: Increase the saving throw’s DC to 16, and the damage to 5d10.