This is important, and I hope italki.com will be able to add these distinctions sooner rather than later. The italki platform is ideal for sign language learners and teachers. My first italki lesson as a student was in American Sign Languages.
It's worth mentioning, that unlike the categories of "slavonic languages" "romance languages" "asiatic languages", sign languages aren't even all in the same linguistic category s each other. For example, sign language in France and the United States are highly related, due to teachers from France teaching in the United States, but unlike spoken English, ASL and British Sign language are unrelated, lexically and gramatically. Just an example, but another reason why they should not all be lumped together under the category "sign language".
Thanks for posting on this topic!