The J (Juliet) and P (Papa) flag semaphores convey the notion of horizontality and verticality conventionally. Either one could be used, I expect:
J (Juliet)
P (Papa)
(From Wikipedia.)
To ward off possible misinterpretations of, for example, the compound "Juliet flag semaphore", the entire communication could be encapsulated and transmitted over the internet using IETF RFC 4824IETF RFC 4824.
Or, for the British mathematicians, this version of Wuthering Heights might clear up any confusion.