Music Staff - https://www.musicstaff.com.br / During a concert at Luna Park in Buenos Aires, Argentina, musician John Mayer picks up a fan's guitar from the crowd and finishes his solo with it. To make the fan's experience even better, John tunes the guitar and signs it before giving it back.

Source: http://www.youtube.com/channel/UCHqz-x3TqpSYpoLHIX7TUHw/videos - Music Staff / https://www.musicstaff.com.br