Deaf-community sign language
A deaf-community or urban sign language is a sign language that emerges when deaf people who do not have a common language come together and form a community. This may be a formal situation, such as the establishment of a school for deaf students, or informal, such as migration to cities for employment and the subsequent gathering of deaf people for social purposes.
Source: Wikipedia — Deaf-community sign language (CC BY-SA 4.0)