In proto-writing, used for inventories and the like, physical objects are represented by stylized or conventionalized pictures, or pictograms. For example, the pictorial Dongba symbols without Geba annotation cannot represent the Naxi language, but are used as a mnemonic for reciting oral literature. Some systems also use ideograms, symbols denoting abstract concepts.
The term "ideogram" is often used to describe symbols of writing systems such as Egyptian hieroglyphs, Sumerian cuneiform and Chinese characters. However, these symbols are logograms, representing words or morphemes of a particular language rather than objects or concepts. In these writing systems, a variety of strategies were employed in the design of logographic symbols. Pictographic symbols depict the object referred to by the word, such as an icon of a bull denoting the Semitic word ʾālep "ox". Some words denoting abstract concepts may be represented iconically, but most other words are represented using the rebus principle, borrowing a symbol for a similarly-sounding word. Later systems used selected symbols to represent the sounds of the language, for example the adaptation of the logogram for ʾālep "ox" as the letter aleph representing the initial sound of the word, a glottal stop.
Many signs in hieroglyphic as well as in cuneiform writing could be used either logographically or phonetically. For example, the Akkadian sign AN (𒀭) could be an ideograph for "deity", an ideogram for the god Anum in particular, a logograph for the Akkadian stem il- "deity", a logograph for the Akkadian word šamu "sky", or a syllabogram for either the syllable an or il.
Although Chinese characters are logograms, two of the smaller classes in the traditional classification are ideographic in origin:
An example of ideograms is the collection of 50 signs developed in the 1970s by the American Institute of Graphic Arts at the request of the US Department of Transportation. The system was initially used to mark airports and gradually became more widespread.