One of my talents is not only to avoid being noticed myself, but to help others to avoid getting noticed as well.
For outsiders, bards seem to have a lot of mystical tricks tied to their performances. Some of these tricks are even mostly unknown among bards. Cloaking is one of the latter tricks. The few who learn this skill are sworn to secrecy, banned from telling anyone about how to do it or even that it is a minstrel trick.
All minstrel tricks use some sort of performance in some way. Usually there's a choice of which type of performance you choose to manifest the effect of the trick. Cloaking, however, is only possible to manifest through humming in a special class of music with strict rules. One wrong note, and the effect is weakened, or even worse; broken. This demands quite a lot of focus from the caster.
Of course, as with any other magical effect, it's not enough to just hum the right melody. There has to be a magical intention behind every tone.
As the caster engulfs themself in magical energy, they are protected against other creatures' eyes. The energy forces the gaze of onlookers to not look directly at the area of effect, as well as distorting the area somewhat so they can't spot it in their side vision either. The humming needed to keep the magical trick going is shrouded in magic as well, making it near impossible to hear for the ones who haven't seen through the effect.
If the effect is still unnoticed by someone outside the area of effect, it's like there's nothing weird going on at all. They might see a tiny flicker in the corner of their eye, but not so intense that people would even think twice about it.
When the effect is seen through by someone outside the area of effect, the creatures inside the area of effect are distorted and wavy, in a way. The low, constant hum that is keeping the effect going can be heard if the listener isn't too far away, though the sound feels more vague than it should be, in a way.
For the creatures inside the effect, the effect itself looks like a translucent shield sphere. Everything outside can be seen as clearly as they could be seen without the effect, though the sphere itself looks like a thin layer of moving fog. The constant hum of the caster is in the background at any time.
(Though the larger area of effect the easier to see through)
Loss of concentration and/or mistakes in the humming will weaken or break the effect.