The legal definition of a trademark is very broad: trademarks are all signs which distinguish a company's goods (products) or services. This broad definition with the reference to all signs means that more distinguishing signs can be protected as trademarks than you perhaps may have thought at first.
The following are a few examples:
- Word marks: The name by which a product or service is on the market.
- Device marks: Logos and labels as well as, for example, words in a special font or presented in a special layout (a logo which includes a name).
- Shape marks: In certain cases, the (three-dimensional) shape of a product or packaging can be a trademark (for example a specially designed bottle of perfume).
- Color marks: In exceptional cases, even a single color or a combination of colors can be a trademark. This is the case when people recognize a certain product or service by its color.
- Sound marks: An advertising jingle is sometimes so well known that when people hear it they immediately know what it refers to. In such cases the sound may be regarded as a trademark and eligible for registration (in the form of a musical stave).
In practice, 99% of registered trademarks belong to categories 1 (word marks) or 2 (device marks).
However, it is also true that not all signs can be trademarks. More information is available here.