I’m an international student from Italy. I don’t have a hearing disability but I learned sign language because a relative of mine does. I’m wondering if I should list it among the languages I can speak. Would it give me an extra point or something?.
No, knowing sign language is not going to give you an extra point. There are plenty of students who take sign language because they are interested in learning. There are students who learn sign language because like you they have a relative or friend whose form of communication is through signing.
There are students who take sign language to fulfill the language requirement because their school offers it as an options. There area students who take sign language as part of their IEP because they may have challenges with speech and language acquisition.
While I agree with @sybbie719 that it will not give you an extra point (nor will speaking Italian, or being multilingual in general), to answer another part of your question, you can list it among the languages you know.
It would be looked upon as any other extracurricular activity or elective class. Put it on your application, however. It is a skill.