When B.F. Skinner wrote Verbal Behavior, he restricted the analysis primarily to vocal behavior and included some discussion of writing. However, the definition of verbal behavior does not specify the response mode at all.
Behavior that has the following features:
It is established and maintained by reinforcement
The reinforcement is mediated by another person
The other person’s action that results in reinforcement must have been specifically trained in order to reinforce speakers
The topography of the behavior: which muscles are used in making the response
Dynamic characteristics of the response: speed, intensity, repetition
Verbal or non-verbal stimulus
Stimulus mode: auditory, visual, etc.
Reinforcement features