“Man is the only animal that blushes. Or needs to.”
― Mark Twain
I don't think sign language will get you out of the requirement for a verbalization spell component, since the somatic movements are their own thing already. But I do recall the original Illusionist in AD&D was the only class which had a few spells for which there were no verbal components at all, such as Hypnotic Pattern, Shadow Door, Wraithform, Rainbow Pattern, Mislead, and possibly Dream (since you have to be asleep). I always thought that was kind of interesting.
