(IDEX Online) - The "courtesy watches" provided by Hublot to its customers have proved to be a victim of their own success.Owners have been so taken with the loan replacements - clearly marked "NOT FOR SALE" on the face - that they've held onto them and forfeited the timepiece they sent for service or repair.The black composite Atelier (French for workshop) with its quartz movement, has become something of a collectors' item."There is an interest in these Atelier watches, as they are not for sale," Ricardo Guadalupe, Hublot chief executive of the LVMH-owned Swiss company, told the FT.Due to dwindling of stocks, the loan watch, launched a decade ago, is now issued only "sporadically in some exceptional cases," he said.A reproduction of the Atelier was made for guests who attended the Fifa World Cup in Brazil, in 2014, without the "NOT FOR SALE".