As a tattoo, the symbolism of the nightingale most likely would be related to the tattoo-wearer's familiarity with romanticist poetry and visual art. In poetry and visual art the nightingale symbolizes love, loss of a love (usually through tragic death, think Romeo & Juliet), longing for love, things like that. For some, I've heard associations with restlessness/insomnia (i.e. discontent with love) because it was believed that the nightingale sang all night long. Hope this helps . . .
It is thought to bring good fortune.
It can often mean lying or deceit or overcoming one of these things.
A cocoon is usually a symbol of transformation; the change from one form to another.
An individual's reason for getting a tattoo is usually personal and unique. A tattoo of a dagger through a hand may be a symbol for a physical or emotional wound that the individual had endured.
A person with a wizard tattoo may attribute many different meanings to it. For example, the tattoo may be symbolic of their status as a pagan or practitioner of witchcraft. Or, the tattoo may have personal symbolism so that it is representative of something like a nickname.