There are two kinds of bards in my world. Those who are simply musicians and storytellers by trade, and those who have learned that music hath charms. All Bards are bards, but not all bards are Bards. Are you following this? Ok, then, now that we got that straight, let's talk about Bards as a player class.
If a bard must cast a spell, the most obvious obfuscation is the song. It wasn't a charm spell that calmed the enraged half-orc you bumped into, he was just so taken with your music that he forgot his anger.
As not all of a bard's spells can be so easily explained, a bard must still be careful.