Shackleton's grave resides on the island of South Georgia and I hear it is the only headstone which faces South. All the other graves there face East as is Christian Custom. The grave contains a nine pointed star.

 Also I've been told there is an inscription on the back of the gravestone by the poet Browning: "I hold that man should strive to the uttermost for his life's set prize".

More Info about the nine pointed star on the grave:

According to the book "Shackleton" by Margery and James Fisher page 485
" his grave had a nine-pointed star which had been very particularly Shackleton's own symbol in his lifetime."
The footnote adds:
Shackleton had a strong streak of superstition in him. He noted that the figure 9 recurred strangely in his life. He had become engaged on the 9th of the month, married on 9th April 1904 and on 9th January 1909 turned north again after his struggle towards the South Pole. He adopted the nine-pointed star as his particular emblem, and he had a silver figure 9 made which was fastened to the door of his cabin on the Quest. By a strange coincidence Lady Shackleton, after many moths of serious illness, died on the morning of the ninth of June 1936.

No doubt someone told you all this ages ago. Your quote from the back of his grave is correct and it does face south
Dorothy Tinkler
A very keen Shackleton fan