LONDON (REUTERS).- On the wall near the exit to the Victoria & Albert’s new show on postmodernism hangs a bright neon sign of the word “Shop”. Many museums are too embarrassed to draw attention to the fact that they force visitors to walk through the gift shop in order to get out of a blockbuster show. Not so “Postmodernism: Style and Subversion 1970-1990”. But then the self referential joke with its bold allusion to consumerism is part of the point. The show, which runs from September 24-January 15, 2012 at the London museum, attempts to do what some commentators believe to be nigh impossible — define postmodernism. The exhibition features works of architecture, painting, music and dance that its curators say fall into the broad remit of postmodernism, a movement they argue consumed itself in the 1980s through its obsession with consumerism and commercial success. “Ultimately this was the undoing of the movement,” said a com