Yes, this is an image from an actual patent filed by Edward L. Van Halen on 30 July, 1985. Here's what it's for:
A supporting device for stringed musical instruments, for example, guitars, banjos, mandolins and the like, is disclosed. The supporting device is constructed and arranged for supporting the musical instrument on the player to permit total freedom of the player's hands to play the instrument in a completely new way, thus allowing the player to create new techniques and sounds previously unknown to any player. The device, when in its operational position, has a plate which rests upon the player's leg leaving both hands free to explore the musical instrument as never before. Because the musical instrument is arranged perpendicular to the player's body, the player has maximum visibility of the instrument's entire playing surface.
Link via Lowering the Bar | Image: US Patent Office