GBA #7: Heart of Oobleck pg. 15
Yes, Dublin can sign. Unovan Sign Language is more common in GBAverse than ASL in reality; I'd like to think that more people know it than not. Dublin's at a disadvantage because, as Coraline says, he has three thumbs and no fingers. But he makes it work.
As for why Dublin never signs around Odina? The two of them jive so well that he doesn't need to.
Chou is an adoptable I got from dragonsushi!
Talk about it in the Discord server!