The term 'Pope's nose' has been around since the 18th century. One of my favourite books is Grose's Dictionary of the Vulgar Tongue (3rd third edition published in 1796) which defined it as "Pope's Nose, the rump of a turkey." Also known as the parson's nose.
My father used the term - to my mother's annoyance, She agreed with Grose that it was vulgar, despite her being a good god-fearing athiest.