A workman jokes besides a work entitled “Monkey Detonator” by Banksy at Bonhams Auction house on September 16, 2011 in London, England. The piece makes up part of the “Urban Art” sale, and is expected to fetch between £70,000 - £90,000 GBP when it goes under the hammer on September 21, 2001 at Bonhams Auction house in London. (Photo by Dan Kitwood/Getty Images)

A piece of work entitled “Black Panther” by Shepard Fairey at Bonhams Auction house on September 16, 2011 in London, England. (Photo by Dan Kitwood/Getty Images)

A Bonhams intern poses with a work by Banksy entitled “Balloon Girl”, at Bonhams Auction house on September 16, 2011 in London, England. (Photo by Dan Kitwood/Getty Images)

A Bonhams intern stands beside a work entitled “Amy” by Cyclops at Bonhams Auction house on September 16, 2011 in London, England. (Photo by Dan Kitwood/Getty Images)

Bonhams interns stand beside a work entitled “Duality of Humanity II” by Shepard Fairey at Bonhams Auction house on September 16, 2011 in London, England. (Photo by Dan Kitwood/Getty Images)

A Bonhams intern stands beside a work entitled “Chinese Soldier” by Shepard Fairey at Bonhams Auction house on September 16, 2011 in London, England. (Photo by Dan Kitwood/Getty Images)