While trademarks have traditionally consisted of a word, logo or some combination of the two, the field has in recent years expanded to include a variety of "nontraditional" marks of various types. Whether these can be protected varies from country to country, and in Cambodia the answer is that they are generally not registerable.
Article 2 of the Trademark Laws defines a "mark" as any visible sign capable of distinguishing the goods (trademark) or services (service mark) of an enterprise. The visibility requirement immediately excludes sound, scent/olfactory, taste/gustatory and touch/tactile nontraditional marks.
More common and more debatable is the question of trade dress or appearance of a product or the packaging itself. For services, this could include the interior and exterior look of a store, or the design of restaurant menu. In Cambodia, while there is no formal, binding legal precedent on the question, the Department of Intellectual Property Rights has generally accepted a broad range of trade dress nontraditional marks in our experience. For instance, General Mills was granted a registration for their "Bugles" snack chip (KH/32149/09):
Similarly, Honda was granted registration for the look of a small engine (KH/25379/06):
And Coca-Cola was granted protection for their iconic bottle design (KH/107/92)
The above examples show that three-dimensional shapes are registerable.
Single color marks, while visible, are generally not registerable, as according to the Trademark Examiner's Manual, marks must consist of "more than one color". The color may be on the goods themselves or on the packaging, and are limited by the needs of competitors to use the color, their being non-functional and non-utilitarian, and must be capable of distinguishing the goods or services from those of competitors.
Moving images, holograms and gestures have also been the subject of trademarks in various countries, but to the best of our knowledge have never been applied for in Cambodia. Whether they would satisfy the "visible" test set forth in Article 2 has yet to be tested.