A photographer takes pictures beside 'Dollar Sign' by Andy Warhol at Sotheby's auction house in London June 8, 2015. The piece has a pre-auction estimate value of 4 - 6 million pounds ($6.12 - 9.18 million) and forms part of a private collection of twenty one works inspired by the US dollar which will be auctioned in London on July 1 and 2. [Photo/Agencies]