Trips Agreement Article 16
All advantages, favours, privileges or immunities granted by a Member shall be excluded from this obligation: 1. Any mark or combination of signs capable of distinguishing the goods or services of one undertaking from those of other undertakings shall be capable of constituting a trade mark. Such signs, including personal names, letters, numbers, image elements and colour combinations, as well as any combination of such characters, may be registered as trade marks. If, by their nature, the signs do not distinguish the goods or services in question, Members may make the registration subject to distinctive character acquired through use. Members may require that the characters be visually perceptible as a prerequisite for registration. 3.