The image used on this t shirt is a simplified version of the Dance of the Orchestra of Death produced by Nicolas le Rouge in 1496. The background ornamentation from the original (shown below) has been removed, leaving only the skeletal musicians which are the focus of the composition.
The piece is one example of a medieval genre more generally described as the Danse Macabre, and intended to remind viewers of their mortality and the insignificance of earthly status in the face of death. They invariably included one or several skeletal figures. We have to remember that the Black Death stalked the population of Europe during this period, and a grisly end was never far away for anyone. So, images of authority are often juxtaposed with those from the peasantry to emphasise the lack of immunity from such visitations for anybody, whatever their position in secular society. The most well known practitioner of this form is Hans Holbein the Younger.
The idea has also passed across to other expressive arts and the French composer Camille San Sans completed an orchestral piece titled Danse macabre (Op 40) in 1874. It is based on an old superstition that death appears at midnight on Halloween and plays the violin, and the skeletons of the dead rise from the grave and dance for him.