Expressive symbolism, at the most basic level, is the use of physical gestures, sounds, artistic symbols, and actions to express personal emotions or reactions to external and internal stimuli. The giggle represents expression that something is funny, or that the person is nervous and uses giggling to release tension. The shaken fist indicates anger or rage that is usually directed at a person who will naturally respond to that basic gesture as one that directly communicates anger.
In the case of neurological disorders or early child development, expressive gestures say something that is internal to the individual, which the individual is compelled to express to the external world, but when the individual has no verbal way of expressing what is going on. Expressive symbolism may come in the form of tics, or inexplicable repetitive actions.
In more ambulatory infants, grabbing both sides of an adults face and turning it, or climbing up on the sofa and grabbing a book out of an adult's hands are excellent expressive symbols that express a need for attention and interaction.
At more complex levels, the symbolic systems for identifying and locating services, facilities, or for providing warnings use simple graphics which can communicate a complete set of concepts and words. Advanced societies only need to look for the stylized silhouette of a figure wearing either slacks or a dress to identify and locate male and female restrooms. Computer users only need to look at a tiny symbol to know that it represents a very complex Internet or computer function that could take a book full of words to explain.
Expressive symbols have a relationship to the concept that they express, whether the relationship is known only to the individual, or to the world at large. Shaken fists, throwing objects, or angry sounds have a direct relationship to internal anger, frustration, or rage. Tears have a direct relationship to pain or some other form of suffering. The wheelchair symbol has a direct relationship to things which assist the handicapped.
Letters of the alphabet, numbers, and other symbols, called "arbitrary symbols" do not have a direct relationship to the thought, object, or emotion. The true test of whether the symbol is arbitrary or not is that arbitrary symbols have to be memorized. A most interesting example occurs when a small child can "count" up to twenty! But when the child is asked to start at the number ten, then finish counting, the child is bewildered and cannot do it. The child has simply memorized a string of arbitrary symbols and has no real comprehension of what those symbols represent.
When the child can relate the number "three" to three objects, then memorization begins, but it will still take a time before there is a complete understanding of numbers and what it is in the real world that they represent.
Expressive symbolism becomes behavior, symbolism, or ritual that directly expresses a concept, feeling, ritual, thought, or idea where there are no verbal or written tools.