Road symbol signs encompass a wide range of things. The shapes of the signs are very important when denoting a specific action. For example, triangular signs clearly indicate a warning and all information contained within tends to be important safety information. Circular signs tend to give information that must be heeded instantly.
Colouring is also important with yellow and orange indicating an impending hazard or a warning. Red indicates danger. Blue, green and white signs give information that is not about a dangerous situation.
There are also numerous graphics used on signs such as skidding cars, people walking and U-turns that are universally recognized symbols without the need for a text explanation.