All languages have a lexicon (vocabulary and expressions) that are understood by users of that language.
In BSL and other sign languages this lexicon can be fixed or productive. The fixed lexical items are often nouns, which can be understood without any context. For example, the BSL sign for ‘dog’.
In the productive lexicon new meanings are created by combining linguistic components following grammatical rules. These will often be visually motivated and may include base signs such as the verbs 'jump' and ‘look’ that can be modified to communicate different meanings.
Typically, signs are developed organically through usage in the community, but sometimes it can be useful to initiate this process and create signs for some technical terms.
Glossaries are often developed as a resource to support people with suggested signs, and to standardise usage. They do this by sharing signs (and sign phrases) already in use that may not yet be widely known; and sometimes by creating new signs, so expanding BSL’s fixed lexicon. However, not all sign variants will necessarily be documented like this.
New signs are usually created by deaf BSL users, who are also subject experts, sometimes working with linguists.