If a bard with Perform (Voice) uses this ability to improve a
- Is the opponent (and other people around) aware of that?
- If so, can the bard use Sleight of Hand to hide the activation?
As a DM, I would start by asking myself, do they know what a bard can do? Much of that will be dependant on the situation, the NPC's in question, the culture of the world they inhabit, and so on. I'd continue with, do they know about that bardic power, "Lore Song"? More importantly, do they have any reason to be watching out for the use of that power? If I have nothing in the makeup of the NPC's to suggest such knowledge, I could just do a skill check to see if they happen to know enough to be looking out for this.
For the sake of argument, let's say they know and are being watchful for such shenanigans. Is there anything to see?
3.5 PHB, page 309
insight bonus: An insight bonus improves performance of a given
activity by granting the character an almost precognitive knowledge of
what might occur. Multiple insight bonuses on the same character or
object do not stack. Only the highest insight bonus applies.
An insight bouns, in and of itself has no visible aura or emissions. It all happens in one's head. Nothing to see there, so let's look more closely at Bardic Music.
3.5 PHB, page 29
Bardic Music: Once per day per bard level, a bard can use his song or
poetics to produce magical effects on those around him (usually
including himself, if desired). While these abilities fall under the
category of bardic music and the descriptions discuss singing or
playing instruments, they can all be activated by reciting poetry,
chanting, singing lyrical songs, singing melodies (fa-la-la, and so
forth), whistling, playing an instrument, or playing an instrument in
combination with some spoken performance.
It looks like some type of noise must be made. It could be a simple as whistling, some DM may allow humming to work, but some sound must be made. The NPC's would be aware of at least that much.
So far as using Sleight of Hand to conceal the "activation". Looking at Sleight of Hand on page 81 of the PHB,
You can cut or lift a purse and hide it on your person, palm an
unattended object, hide a light weapon in your clothing, or perform
some feat of legerdemain with an object no larger than a hat or a loaf
It seems that, RAW, one would not be able to conceal the use of voice with Sleight of Hand. It's not made to be used that way. That's not saying the bard couldn't try to use a low volume to activate Bardic Music, but it would not fall under Sleight of Hand, RAW. The DM may judge that an INT check could be made to make less sound but that would depend upon the DM's judgment.