Hi! Hope you're doing well. I was reading a fantasy webcomic with some Deaf characters and was wondering: what adjustments to the language creation processes would a conlanger have to make for creating a sign language? Thanks!
The short answer is relatively few. Sign languages are languages and do all the same things with a different phonology. So long as you understand the phonology of a sign language you can create a sign language.
The long answer is here. That's a thing I wrote up called SLIPA (Sign Language IPA). Due to the fact that the potential for iconicity with gesture is greater than with sound there's a lot more onomatopoeia in a sign language than in a spoken language. To explicate, onomatopoeia in spoken language is a word that imitates the sound of the referent (splash, crash, plunk, boing). In a sign language, it's a sign that imitates the look of the referent (ASL TREE, for example). Since it's possible to be more iconic, sign languages take advantage of that fact. Consequently, you don't find sign languages that DON'T take advantage of it and are purely abstract. There are also things that are hard or impractical in a spoken language that are simple in a sign language simply due to the medium (e.g. full number incorporation in the ASL words for WEEK and MONTH). Finally, there are a lot of "on the fly" verbs that are created that have no obvious analog in a spoken language. It's something like the sentential words of a polysynthetic language combined with imitative sounds in a spoken language to describe a body in motion.
In other words, because there are things you can do in a sign language simply due to the medium that you can't do in a spoken language, sign languages often do those things. It would be strange (i.e. non-human) if they didn't. If you're aiming to create a secret sign language, perhaps you intentionally don't take advantage of those things. It's possible to create a purely abstract sign language, but it would be a fairly obvious construct the way Ithkuil is very obviously not a plausible human language (i.e. it could never have evolved naturally to be the way it is). This might be a fun thing to do for a fictional setting—a totally non-iconic sign language created for secret communication. This is, essentially, what I did with the Atreides sign language in Dune (as opposed to the other sign language I created for the first film that wasn't used). Even that one, though, takes advantage of iconicity in a way that a truly abstract sign language need not. This is because part of the secrecy of the language is the way it's used. Others aren't even supposed to see it—and if they do, they're supposed to dismiss it as hand twitches. You could make an obvious sign language (i.e. it's obvious these characters are signing to each other) but with really, really weird associations—like pointing to your interlocutor means "sky", where eveyrone looking on will think it means "you".
Anyway, just some thoughts. This is an underexplored area of conlanging, but due to the simplicity of video creation and sharing nowadays, it's something that's worth exploring. Back in 2006 when I wrote up SLIPA it wasn't practical to take videos and upload them. It was possible, certainly—we had high speed internet and websites—but we didn't have smartphones, I don't think YouTube existed yet, most frontend UI didn't have video embedding as a feature of its platform, etc. We were lightyears ahead of the internet as we understood it in the 90s, so 2006 would be much more familiar to the people of 2024 than the people of 1994, but smartphones and social media (and its infrastructure) really changed the nature of capturing and sharing video. Conlangers have taken advantage of that in every way EXCEPT creating, documenting, and sharing CSLs (created sign languages).
Like (I don't want to go off on a tangent here) you can have an entire YouTube account that is just a dictionary. ASL already does this. Go on YouTube and type "ASL sign for [whatever]". There are tons of videos that are like 10-15 seconds long that are just demonstrations of a single sign from different angles, all made by Deaf signers. And the videos don't need sound! You don't have to worry about audio quality, microphones, etc. You can actually use YouTube to document an entire sign language. No one's done it yet. Why not?
Anyway, those are my thoughts. Hope this helps.
