Signed languages like many spoken languages around the world have been an "oral" culture (other than video as a recorded form) until a relatively recent time. However, writing systems for signed languages have been attempted many times long before.
Developed by Adrean Clark, ASLwrite. Used with permission.
The earliest record of a method of writing signs was a book, "Mimographie," which was published in 1825 by Roch-Ambroise Auguste Bébian (1789-1839). Bébian was a hearing man who was native-like fluent in French Sign Language.
Deaf people have been exprienced oppression of their language and human rights for the past thousands of years except for the short golden period prior to the infamous Milan of 1880. This oppression hindered and delayed discoveries and innovations until the 1960s, which since then has bloomed.
Among these many exciting discoveries and historical revolutions (from ASL linguistics to neuroscience studies) since the 1960s, writing systems for ASL have recently emerged over past few decades, such as ASLwrite (public domain), si5s (2010), ASLphabet (1990s), SignWriting (1970s), and other earlier notations, such as Stokoe Notation (1960s) Hamburg Notation System a.k.a HamNoSys (1985), mostly developed by ASL linguists (ASL Font). These notations such as Stokoe Notation and HamNoSys were used for linguistic purposes.
With the ASL writing systems recently emerged during the last few decades, the ASL community has gradually come to accept the idea of writing ASL. The use of an ASL writing system has been gradually growing among bilingual and monolingual ASL speakers.
Adrean Clark of ASLwrite established a website in 2011 and published How to Write American Sign Language. This writing system is freely open to the public domain. Robert Arnold Augustus and ASLized published The Official American Sign Language Writing Textbook. (si5s) in 2013. The si5s and ASLwrite writing systems are two branches of a common root.
Another writing method SMYLE (an abbreviated term for Signographie Manuscrite YaelLE) was invented by Yaelle Pierrat-Struck in 1997.
Regardless of the writing systems, it's a Deaf community that will evolve a writing system and its digits to the highest potential of writing. No writing system will be official for the next years to ensure that it gives the Deaf community a room to experiment and evolve some digits to the highest efficient usage.
"ASL Font: Ways to Write ASL" http://aslfont.github.io/Symbol-Font-For-ASL/ways-to-write.html
Augustus, Robert Arnold, et al (2013). The Official American Sign Language Writing Textbook. si5s and ASLized.
Clark, Adrean. "ASLwrite." www.aslwrite.com.
Wikipedia. "Roch-Ambroise Auguste Bébian" http://en.wikipedia.org/wiki/Roch-Ambroise_Auguste_B%C3%A9bian
Why sign language writing?
ASL calligraphy from signing to writing
Experimenting with digits: a sandbox
Introducing ASL writing. ASL Writing Dictionary