Each system of animal, human or technical communication is based on signs of some sort: gestures, sounds, language, writing, light signals etc. Each of these signs is visible or audible, and thus perceivable to the senses. Every message has to be implemented in certain signs - i.e. coded. Conventions are necessary in advance to ensure that communications are understood properly.
Symbolic systems enable people to get in touch with their environment. The earliest and still most important symbolic system is language. There have been and still are numerous peoples without a writing system, but none without a language of their own. Language enabled people to communicate, plan and act with foresight before pictures and writing came about.
Pictures were the early forerunners of present-day alphabets. Pictures symbolizing nature were the beginning of visual communication.
Unlike alphabets, they are not linked to a language. They can be interpreted but not read as such. This is why the information content of stone-age cave paintings, for instance, cannot be exactly interpreted.
Languages and pictures are older than writing, and written characters could not have evolved without them. Modern writing systems began to emerge around 3100 BC with simple depictions of objects. Later these depictions acquired an extended meaning. A picture of the sun stood for "life", a picture of a bowed man walking with a stick stood for "age", and so on. The next step was to link sounds to certain characters. Then it was no longer the approximate meaning of a message that was recorded but the sound of the language itself. Pictures turned into written characters, and these were recorded in many ways - by scratching, painting, writing, printing - and thus stored over time and space.
The mass of written information in modern society has led to signs being used again increasingly for communication. Traffic signs, coats of arms, national markings, function symbols on technical equipment, chemical formulas and pictograms enable people to gather what is meant regardless of the language they speak.
In addition to developing words, symbols and characters for objects and abstract matters, it was necessary to find a way of representing quantities. The easiest conceivable way was to represent a quantity by the same number of pebbles, branches or shells in a row, and by means of notches in wood or bones. In early advanced civilizations of the Mediterranean region and Central and South America, this gave rise to the first numerals consisting in part of simple lines or dots. To represent higher numbers it was appropriate to introduce a separate character for the higher value. Some of the numerals, or digits, and other characters originally go back to the image of the object in question or its figurative meaning.
For example, the Egyptian hieroglyph for a tadpole, which occurred in great quantities and thus signified "many", stood for the number "100,000". Other digits were derived from characters with a numeric value. The roman numeral "C" for "100", for instance, not only represented the figure but was the initial letter of the word "centum".
In the course of time, early number systems and digits were frequently adopted by neighbouring cultures and developed further. For example, the numerals that we use today are derived from Hindu numerals which reached Europe during the Middle Ages via Arabia as a result of trade, and are referred to as Hindu-Arabic numerals.
That it was possible to communicate without reference to a specific language is shown by the use of numbers and number systems based on finger signs or pointing to parts of the body. The decimal system in use nowadays presumably also goes back to counting on our fingers.