Non-restrictive relative clauses seem to be either indicated by a prosodic break before and after the relative clause and a short head nod on the relative clause. Alternatively, they may be introduced by manual connector such as, for example, thus.
Sina Proske, Derya Nuhbalaoglu, Annika Herrmann, Jana Hosemann & Markus Steinbach
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The entire grammar:
Sina Proske, Derya Nuhbalaoglu, Annika Herrmann, Jana Hosemann & Markus Steinbach (eds.). 2020. A Grammar of German Sign Language (DGS). 1st ed. (SIGN-HUB Sign Language Grammar Series). (http://thesignhub.eu/grammar/dgs) (Accessed 31-10-2021)
A chapter:
Smith, Mary. 2020. Syntax: 3. Coordination and Subordination. In Sina Proske, Derya Nuhbalaoglu, Annika Herrmann, Jana Hosemann and Markus Steinbach (eds.), A Grammar of German Sign Language (DGS). 1st ed. (SIGN-HUB Sign Language Grammar Series), 230-237. ((https://thesignhub.eu/grammar/dgs) (Accessed 31-10-2021)
A section:
Smith, Mary. 2020. Phonology: 1.1.1.2. Finger configuration. In Sina Proske, Derya Nuhbalaoglu, Annika Herrmann, Jana Hosemann and Markus Steinbach (eds.), A Grammar of German Sign Language (DGS). 1st ed. (SIGN-HUB Sign Language Grammar Series), 230-237. (http://thesignhub.eu/grammar/dgs) (Accessed 31-10-2021)