In recent times holograms have been increasingly used as trade marks in the marketplace. However, it has traditionally been difficult to protect holograms as trademarks through registration, as a hologram was not considered to be a 'trademark'. This issue was addressed by the World Trade Organization Agreement on Trade-Related Aspects of Intellectual Property Rights, which broadened the legal definition of trademark to encompass "any sign...capable of distinguishing the goods or services of one undertaking from those of other undertakings" (article 15(1)).