August 18, 2012
Here is a PDF document listing the ISO encoding for World Scripts. You will find SignWriting on page 5:
>> Hello Maria and everyone on the SignWriting List!
>> On October 10, 2006, SignWriting was registered as one of the "World
>> Scripts", by the International Bureau of Standardizations (ISO).
>> Go to:
>> ISO 15924 Registry of World Scripts
>> and scroll down.
>> SignWriting is categorized as:
>> Sgnw, 095, SignWriting, SignEcriture, 2006-10-10