From the Patch 3 notes:
Fixed NPCs not reacting to Hunter's Mark as a hostile action.
Casting the Ranger spell Hunter's Mark is not a perceptible hostile action. Text of the spell:
You choose a creature you can see within range and mystically mark it as your quarry. Until the spell ends, you deal an extra 1d6 damage to the target whenever you hit it with a weapon Attack, and you have advantage on any Wisdom (Perception) or Wisdom (Survival) check you make to find it. 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 a new creature.
This was addressed by WoTC Sage Advice:
https://twitter.com/Dan_Dillon_1/status/1192204453786476544@Dan_Dillon_1 If someone casts Hunter’s Mark, or really any similar spell with no particular visual cue (like the sparkle of Faerie Fire), does the target know they’re under the effect of a spell?
Do you know if you're affected by a spell?
Not necessarily! Only if the spell has observable effects (fireball), or the description tells you that you realize magic was used (charm person).
Check out pg 12 in the Sage Advice Compendium! #dnd #WotCStaff
From the aforementioned Compendium:
Do you always know when you’re under the effect of a spell?
You’re aware that a spell is affecting you if it has a perceptible effect or if its text says you’re aware of it (see PH, 204, under “Targets”). Most spells are obvious. For example, fireball burns you, cure wounds heals you, and command forces you to suddenly do something you didn’t intend. Certain spells are more subtle, yet you become aware of the spell at a time specified in the spell’s description. Charm person and detect thoughts are examples of such spells.
Some spells are so subtle that you might not know you were ever under their effects. A prime example of that sort of spell is suggestion. Assuming you failed to notice the spellcaster casting the spell, you might simply remember the caster saying, “The treasure you’re looking for isn’t here. Go look for it in the room at the top of the next tower.” You failed your saving throw, and off you went to the other tower, thinking it was your idea to go there. You and your companions might deduce that you were beguiled if ev- idence of the spell is found. It’s ultimately up to the DM whether you discover the presence of inconspicuous spells. Discovery usually comes through the use of skills like Arcana, Investigation, Insight, and Perception or through spells like detect magic.
So I hope this change will be re-evaluated.
BTW loving the game!
