There’s a perfectly good explanation for why several plaster noses appear randomly around London's Soho neighborhood. However, the urban legends that have bubbled up around the mysterious sculptures may be even better.
In 1997, with the proliferation of CCTV cameras spawning a controversy in the UK in general and London in particular, artist Rick Buckley undertook a project to critique the spread of "Big Brother" society. Inspired by the Situationists — a mid-century artists' group with a flair for avant-garde performative works — Buckley made 35 plaster of Paris casts of his own nose and affixed them to buildings scattered around London. Targeting well-trafficked areas and important public buildings like the National Gallery and Tate Britain, Buckley installed his guerrilla artworks right "under the nose" of the burgeoning surveillance state.
He painted the noses to match the walls they were affixed to and did not publicize his project whatsoever, curious to see if he could execute his plan without being detected and hoping that the unnoticed noses would simply become part of the structures themselves. Most of the noses were discovered fairly quickly and removed, but for those few that remained, he accomplished his goal — with some unintended consequences.
Buckley didn't publicly claim responsibility for the noses until 2011, allowing 14 years for the new architectural details to generate origin stories ranging from the misguidedly speculative to the endearingly fantastic. What is perhaps the best-known legend refers to the Seven Noses of Soho, and states that if you manage to find all seven of the mysterious noses hidden around London's historic entertainment district you will become fabulously wealthy (sources provide confirmation of only five noses in Soho and one of them is not a Buckley nose, so the prize still awaits intrepid treasure hunters). Another myth took the noses to be original and claimed that London architects used to be in the practice of including casts of their noses on their finished buildings.
A number of legends revolve around one nose in particular: the one stuck to the Admiralty Arch that leads from the Mall to Trafalgar Square (often included among the Soho noses, though it is technically not in Soho). One story stated that it was put there to mock Napoleon, fixed at a height that allowed cavalry troops to tweak it as they passed under the arch. Another held that the nose is a nod to the Duke of Wellington, who was famous (among other, more world-historical accomplishments) for possessing a very large schnoz.
The most amusing myth is that the nose is a potential spare for the memorial statue of Admiral Lord Nelson that stands atop a column in Trafalgar Square. Apparently there was concern that the uppermost extremity of Nelson’s likeness would be damaged when the statue was lifted to the top of the high column, so a spare was stashed on the arch. Not bad histories for a nose that didn't exist until 1997.
If you’re interested in this particular anatomical tour of London, a quick Google search and the accompanying map should get you started on the known, confirmed nose locations. There are also an unknown number of ears hidden on various buildings around Covent Garden. The ears are thought to be installed by another sculptor, only this time for no apparent reason.