This is an homage to the real-life "Indian-head" test pattern, introduced in 1939 and widely used during the era of black-and-white television in America.

The reason the man's head was included in the test pattern was to allow the tuning of brightness and contrast settings, either by broadcast engineers to ensure broadcasts were being sent correctly, or by TV owners and repair shop technicians to ensure broadcasts were being received correctly.

I don't know why the head was specifically that of a Native American man, but the intricate detail of his headdress, incorporating multiple shades of grey, certainly makes it a striking (and useful) test image.