Could be used to express 1 bit of information in some non-obvious convention.

The x86-64 ISA provides a lot of alternative encodings for the same instruction or for instructions that are equivalent.

It has already been suggested to use these for steganography, i.e. for embedding a hidden message in a binary executable file, by encoding 1 or more bits in the choice of the instruction encoding among alternatives, for every instruction for which alternatives exist.

The shareware assembler a86 used to use this to fingerprint its output so the author could check whether random programs to see if they were assembled using it without having paid the shareware fee.