Charm Person comes to mind.Wouldn't that depend on the spell? But I thought most spells have an effect if it hits and works.
A creature that successfully saves against a spell that has no obvious physical effects feels a hostile force or a tingle, but cannot deduce the exact nature of the attack. Likewise, if a creature’s saving throw succeeds against a targeted spell you sense that the spell has failed. You do not sense when creatures succeed on saves against effect and area spells.
Not necessarily. Supernatural abilities don't follow the same rules as spells. As I mentioned above the text you've found sets a precedent for how things usually work, but is not an official answer to your original question.This would still apply to a Hexblade's curse right? The curse is a supernatural ability that basically mimics the spell Bestow Curse, just that it doesn't have the options, and it's power scales as you level.
I'm playing a hexblade, and when using my hexblade curse, the DM ruled that there was no way I could have seen the curse take effect, so I couldn't tell if it worked or not. Is he right?
The hexblade's curse just give -2 to a bunch of rolls. Not necessarily obvious to the naked eye.Most Bestow Curse effects should be obvious.