  It is a frequent assumption that - via superluminal information transfers -
superluminal signals capable of enabling communication are necessarily
exchanged in any quantum theory that posits hidden superluminal influences.
However, does the presence of hidden superluminal influences automatically
imply superluminal signalling and communication? The non-signalling theorem
mediates the apparent conflict between quantum mechanics and the theory of
special relativity. However, as a 'no-go' theorem there exist two opposing
interpretations of the non-signalling constraint: foundational and operational.
Concerning Bell's theorem, we argue that Bell employed both interpretations at
different times. Bell finally pursued an explicitly operational position on
non-signalling which is often associated with ontological quantum theory, e.g.,
de Broglie-Bohm theory. This position we refer to as "effective
non-signalling". By contrast, associated with orthodox quantum mechanics is the
foundational position referred to here as "axiomatic non-signalling". In search
of a decisive communication-theoretic criterion for differentiating between
"axiomatic" and "effective" non-signalling, we employ the operational framework
offered by Shannon's mathematical theory of communication. We find that an
effective non-signalling theorem represents two sub-theorems, which we call (1)
non-transfer-control (NTC) theorem, and (2) non-signification-control (NSC)
theorem. Employing NTC and NSC theorems, we report that effective, instead of
axiomatic, non-signalling is entirely sufficient for prohibiting nonlocal
communication. An effective non-signalling theorem allows for nonlocal quantum
information transfer yet - at the same time - effectively denies superluminal
signalling and communication.
