But you're getting into all sorts of TV conventions there. German TV conventions at that. The inclusion of a character 'speaking' DGS doesn't necessarily mean that character's speech is intended to be understood by sign-speakers, any more than the inclusion of a German-speaking character in English TV means that character is intended to be understood by German speakers. As I watch very little TV, I can't think of an English-language example, but I know of a Polish series in which one of the major characters is meant to be American. The actor is of course Polish and watching it, you would laugh at her English, full of inaccuracies and weirdly accented. You'd also notice that the 'errors' in her Polish were never enough to inhibit understanding by Poles and tend not to be ones actually made by English speakers attempting Polish (or at least you would notice this if you also spoke Polish!). But as the intended audience isn't English speaking, it doesn't matter. Similarly, the Germans in any British or American war film, whose German is Englisch schpoken leik zat. So with these deaf characters, quite likely. After all, if the series was to be aimed at speakers of DGS, every character would have to be signed. Or more likely, there would be captions (what's the German for SDH?)