It uses SignWriting, which is currently the most popular proposal for a sign language writing system. SignWriting does have Unicode support, but nevertheless this Wikipedia Incubator is kinda buggy for me.

Although I’ve long been familiar with SignWriting, the way I personally would’ve imagined a SL wiki working would’ve been a sort of programmable animation that anyone can edit, maybe even a bit like a Scratch project. Because although SignWriting is the most popular SL writing system, it’s far from universally accepted, and not all signers are going to be literate in it. Though I suppose endorsement from the Wikimedia Foundation might very well be what it takes for SignWriting to reach that critical mass for widespread adoption, if the ASL Wikipedia Incubator ever becomes graduated to an actual full-fledged ASL Wikipedia.