This is off-topic, but it depends what you mean by "read" and by "most." In my research I've seen Deaf people with very low reading abilities in spoken languages. As I understand it, they are representative of the majority of Deaf people, even in literate countries like the United States.
More on topic, in American Sign Language and Mexican Sign Language, there are major differences between ad hoc borrowings and fully lexicalized signs, and the lexicalized signs don't always correspond to what signers may have been reading. So Trevor's point about this unnamed sign language is valid: the fact that it distinguishes between the three concepts is evidence that the distinction is not confined to one community.
--
-Angus B. Grieve-Smith