The electronics company was convinced it was being cheated. It even asked for a pounds 60,000 refund from the distributor after finding that 12 per cent of the sites were empty.
But gradually distrust turned to delight. In fact, the posters had become collector's items. So far about 3,000 have been stolen. The thefts started near university campuses at Edinburgh, Liverpool, Birmingham and Bristol, leading to suspicion that students were responsible.
The distributor, More O'Ferrall Adshel, was less happy. In dozens of cases the 6ft by 4ft posters were removed by smashing plastic display panels in bus shelters. Each shelter costs about pounds 2,500 to repair. In most incidents, however, the thieves had worked out how to trip spring-loaded locks.
The five posters in the campaign feature pictures of footwear - a brogue, a stiletto, a tennis shoe, a flipper and a boot - each in the shape of a face. Some people believe the shoes are caricatures - John McEnroe as the sports shoe and Grace Jones, the singer, as the black stiletto.
Oliver Lewis-Barclay, account director of the advertising agency Bartle Bogle Hegarty, said: 'We believe students are taking them for their bedroom walls - hopefully they have become a bit of a cult item.'
Chris O'Donnell, of Adshel, added: 'We are pleased that the campaign is getting a good reaction, but our repair department is not so delighted.'
Less rebellious members of the young generation have been writing to Sony, which is giving away copies of the posters.