A feature of all national sign languages is the use of the gestural-visual channel in the transmission of information and not the vocal-auditory channel, as in the case of audio languages. Sign languages have no morphological systems, which in practice is manifested by the lack of variety of signs for cases, types and people. This results in the use of positional grammars, where the order of the words determines the meaning of the sentence. The other characteristics of sign languages are identical to those of spoken languages.
Sign languages are efficient communication systems that allow the free transmission and reception of information. The necessary condition for the emergence of such a permanent communication system that is transmitted from generation to generation is the existence of a community in which it is necessary to create it.
Because language – regardless of the form of its use – is a social phenomenon, created by the human community and for its needs. Deaf people, also known as deaf or deaf people, have become such a community for sign language. A common feature of sign languages, unlike auditory languages, is that they have more similarities to reality than audio languages.
In the latter, we sometimes deal with the so-called onomatopoeia, when the shape of a word imitates its content, for example in the words noise, whistle or crepitus. For obvious reasons, there are very few of them. In sign languages, on the other hand, very often there are signs that mimic the shape of a specific object or movement performed for a specific activity. These signs, called iconic signs, make up on average about 1/3 of the number of all signs in a given sign language. Due to the high iconicity index, the sign languages of the different countries are similar to each other.