A nose was an sensory organ associated with smell.
When Amy, Rory and River Song exited the TARDIS after it landed in the Oval Office, the Eleventh Doctor introduced them to President Richard Nixon as his top operatives: the Legs, the Nose, and Mrs Robinson. (TV: The Impossible Astronaut)
When the Curator said "Who knows?" to the Eleventh Doctor, he tapped the side of his own nose when he said the word "nose". (TV: The Day of the Doctor) This was a mannerism also displayed by the Fourth Doctor. (TV: Robot, The Brain of Morbius, The Creature from the Pit )