Basically symbolises an inability for anyone to find anything within the Brave New World:
John especially seeks many things throughout the novel, he moves away from society to seek truth and art. However his suicide is a representation the fruitlessness of this action.
If you could imagine someone looking for something with a compass as a guide, they would turn, from North, all the way South in order to find it. By turning backwards to North, Huxley is expressing that nothing has been found.
there's more on it here if you're interested:
'Brave New World' (Aldous Huxley) Quote Analysis? - Yahoo! Answers
