*Ciphers* are orthographies designed (ideally) to map one-to-one
against graphemes of a writing system and (ideally) are designed
to obscure those graphemes by using non-obvious forms to hide
content from casual observers.
I don't think whether a system was "designed to obscure the graphemes" is important (at least in respect to whether Unicode should encode a script or not). Some discussing this seemed to think it was.
For example Morse code, semaphore flags, braille, and bar codes are often implemented in fonts as one-to-one transliterations of the corresponding Latin characters. But these systems were not at all designed to obscure the graphemes to which they point, but to reveal their semantics clearly in situations where normal representations of the original graphemes were not as usable.
Perhaps rather than "cipher" one should say that Unicode does not encode separately scripts or systems intended solely as transliterations of other scripts. Ciphers are a common example of such scripts and systems.
Jim Allan
