Sign language differs from oral language in its relation to writing. The phonemic systems of oral languages are primarily sequential: that is, the majority of phonemes are produced in a sequence one after another, although many languages also have non-sequential aspects such as tone. As a consequence, traditional phonemic writing systems are also sequential, with at best diacritics for non-sequential aspects such as stress and tone.
Sign languages have a higher non-sequential component, with many "phonemes" produced simultaneously. For example, signs may involve fingers, hands, and face moving simultaneously, or the two hands moving in different directions. Most writing systems have not been designed to deal accurately with this level of complexity, although the Sutton SignWriting script has succeeded.
In those few countries with good educational opportunities available to the deaf, many deaf signers can read and write the oral language of their country at a level sufficient to consider them as "functionally literate." However, in many countries, deaf education is very poor and / or very limited. As a consequence, most deaf people have very little to no literacy in their country's spoken language. There are Deaf people who do not see a need to write their own language.
However, there are some scripts for sign languages, with one in particular being used in 40 countries (Sutton SignWriting). SignWriting, developed by Valerie Sutton in 1974, is a practical and by far the most popular system for recording the movements of ASL as well as any signed language around the world. Volumes of written ASL have been recorded to date [www.signwriting.org]. The SignWriting script can be used for detailed research, daily use as well as shorthand. SignWriting has adequate means of handling mouthing, facial expression and dynamics of movement. The Stokoe notation, devised by Dr. William Stokoe for his 1965 Dictionary of American Sign Languageis an abstract phonemic alphabet. Designed specifically for ASL, it is limited in that it has no way of expressing facial expression. The more recent ASL-phabet is a minimal derivative of Stokoe along the lines of shorthand. The Hamburg Notation System (HamNoSys), developed within the last several years, is a detailed phonetic system, not designed for any one sign language, and intended as a transcription system for researchers rather than as a practical script.
These systems are based on iconic symbols. Some are pictographic, being conventionalized pictures of the hands, face, and body; others, such as the Stokoe notation, are more iconic. Stokoe used letters of the Latin alphabet and Arabic numerals to indicate the handshapes used in fingerspelling, such as 'A' for a closed fist, 'B' for a flat hand, and '5' for a spread hand; but non-alphabetic symbols for location and movement, such as '' for the trunk of the body, '×' for contact, and '^' for an upward movement. David J. Peterson has attempted to create a phonetic transcription system for signing that is ASCII-friendly known as the Sign Language International Phonetic Alphabet (SLIPA).
SignWriting, being pictographic, is able to represent simultaneous elements in a single sign. The Stokoe notation, on the other hand, is sequential, with a conventionalized order of a symbol for the location of the sign, then one for the hand shape, and finally one (or more) for the movement. The orientation of the hand is indicated with an optional diacritic before the hand shape. When two movements occur simultaneously, they are written one atop the other; when sequential, they are written one after the other. Neither the Stokoe nor HamNoSys scripts are designed to represent facial expressions or non-manual movements, both of which SignWriting accommodates easily.