Can you tell if someone transfers Hunter's Mark or Hex after the original target is reduced to 0 HP?

Question

The spells hunter's mark and hex both include this clause:

If the target drops to 0 hit points before this spell ends, you can use a bonus action on a subsequent turn of yours to [mark/curse] a new creature.

Both of these spells have spellcasting components that would be observable to another creature when the spell is initially cast. If I want to mark or curse someone, anyone nearby will know.

If the original target is reduced to 0 HP, is it observable in any way should the caster choose to transfer their mark/curse to another creature? Or is this essentially untraceable after the initial casting?

Obviously for this question, I am ignoring a sorcerer's Subtle Spell metamagic. We can also assume that this is not from stealth; the caster is not trying to hide what they are doing, this is more about whether or not there is anything to hide beyond the initial casting.

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Related:

• Is a creature aware that a Hex or Hunter's Mark spell has been cast on it? (but related to the initial casting from stealth)
• Are Hunter's Mark and similar spells noticeable to the target? (duplicate of the above, still about the original casting)
• Does moving the curse from the Hex spell to a new target have any spell components? (regarding if the transferring part requires components)

Answer 1

Only through Detect Magic or a similar spell/feature

As covered in this question, Hex does not require components when moved to a new creature. A creature cannot recognize that Hex has been moved by observing the spellcaster fulfilling the component requirements.

There are features, however, that allow creatures to detect magic, the most obvious example of which is the spell Detect Magic. A creature using this spell or benefitting from a similar effect would be able to perceive the magic of Hex on the new target.

Since Hex and Hunter's Mark use similar wordings to describe moving the effect to a new creature, Hunter's Mark would also be undetectable when moved, except through Detect Magic or a similar feature.