Amberlight's Combusting Sigil

You imbue one target you touch with a transparent rune. The effect of the spell may differ if the target is a creature or an object:

Creature: If the creature is aware that the rune is placed on it, it can make a wisdom (perception) check against your spell save DC. If it succeeds the creature is aware of the rune's location and if it fails it can ask for an ally to make the same check until the rune is found. You may use your action to trigger the rune at any time if you are in the same plane of existence. If the rune is triggered the creature must make a constitution saving throw or take 32 (8d8) fire damage plus another 4 (1d8) fire damage for each hour the rune was on the creature without being triggered (up to a maximum of 48 [12d8] fire damage). The creature takes half damage on a success.

Object: The rune can be placed on any object. A creature holding the object can make an intelligence (investigation) check against your spell save DC in order to find the rune. You may use your action to trigger the rune at any time if you are in the same plane of existence. If the rune is triggered it explodes, forcing any creature that is touching the object to make a constitution saving throw against your spell save DC. On a failure, the creature takes 32 (8d8) fire damage. Plus another 4 (1d8) fire damage for each hour you held the object without triggering it (the extra damage only goes up to a maximum of 48 [12d8] fire damage). On a success the creature takes half damage. The object itself also takes damage from the spell.

The rune can be dispelled by spells such as dispel magic and greater restoration.

When you cast this spell using a spell slot of 6th level or higher, the damage maximum of the spell increase by 2d8 for each slot level above 5th.