In 5th Edition which spells, like Suggestion, are not noticable, and which are noticeable by the target and/or nearby onlookers?
Are there differences if a target fails or succeeds on a save roll?
I noticed only a few Enchantment spells mention a comment on it, like 'Charm Person' or 'Friends'.
Currently playing a Knowledge Domain Cleric with a different GM; please expand the answer to include Channel Divinity: Read Thoughts/Suggestion ability & spell combination. (The cleric ability which allows Suggestion to succeed automatically).
I'm Hungarian and very new to 5th edition.
Best Answer
Unless the description states the target is aware of the spell, it is not automatically aware by default.
Spells only say what they do. If a target knew it was under the effects of a spell any time a spell was cast on it, then illusion spells would be wholly useless.
Since your question is about charms/enchantments, it's worth pointing out that these spells explicitly state when a target is aware. For example, Friends states the target knows it was magically compelled. Charm Person also states this.
An example of a spell that doesn't state this is Geas. At no point does it say that the affected creature is aware that it is under magical compulsion to obey the command. This is important because if you happen to be a Sorcerer, you could cast this as a subtle spell and the affected target would have absolutely no way to tell it had even been targeted by a magical effect.
By and large, the default for all magic effects is that something is unaware until they discover it through some mechanism. For instance, you would automatically see a fireball coming at you because it's not a hidden object. Whereas you may not notice a delayed blast fireball that's hidden above a door jamb as you passed under it. Other methods of discovering a spell is affecting you are things like, "Hey, the whole world is getting a lot bigger! Hmmmm.... I might be getting shrunk by an enlarge/reduce spell." Or, "How come I have hooves and oh my god I'm a goat." when targeted by a polymorph.
At the end of the day, the question you need to ask is, "Does the spell explicitly state that the creature is aware?"
Worthwhile contribution from Rubiksmoose: