Inside the soundhole, you find a piece of paper with some writing:

Legend of the White Horse

In a world full of desert, a white horse travelled the land. This white horse was known throughout the land to stop the injustices it witness. He had a name based upon his speed and the people thank him for his existence. 

Gives advantage on any performance checks. This item can be used as a weapon only during a surprise round and player with item must go first for bonus. If player rolls a natural 20, player can do 4d6 of damage, if not then 2d6 of damage. Guitar also magically repairs itself. 

Gives advantage on any performance checks.