It is incorrect to think of Sign as a gestural approximation of oral language. The inherent structure of Sign languages affords Signers as much improvisation as the deep structure of oral language makes improvisation part and parcel of oral or written communication. The impression that Sign language is universal is wrong. For instance, American Sign Language, French Sign Language, Aborigine Sign Language and Irish Sign Language are very different from one another. 

Signers, especially if they have learned Sign as a primary language, even think and dream in Sign and in some instances, Sign while thinking audibly or dreaming. A friend, who lost hearing well into adulthood, told me recently that the dreams of the post-lingual deaf are remarkably loud. This must be because the mind remembers sounds and voices from the hearing past.

Since Signers can eavesdrop on other Signers at a peer gathering, there are etiquettes about separate groups avoiding listening in to conversations of others. This is the official line. There must be some nosy parkers among Signers too. How do they pry? Peepdrop? Of course, moral conditioning of one’s eyes to things to be averted is routine politics of daily experience. But what, to hearing persons, must be extra-ordinary about the cultural grounding of Signers’ eyes is that it is sociolinguistic as well. 

There is an interesting parallel at the neurological level — or, isn’t it a convergence? — between Signing and oral language as praxis. Just as oral language users with cerebral impairment — for instance,  lesions in the left hemisphere of the brain following a stroke —  can become victims of aphasia (loss or impairment of speech or ability to understand language or, both), Signing aphasia occurs in similarly afflicted Signers!   

There is much more to Signing than is dreamt of in insignate philosophy. ‘Deaf and dumb' is grossly incorrect. ‘Deaf and mute’ is a sight nearer. Somewhat.