In reply to H Peacock, referring to the OP's original post, the whole point of the post is that "Join left downwind" is ambiguous, how does this convey that the cct is "Clearly RH"?
It is difficult not knowing if there was any prior communication, especially if ATC knew position of plane relative to cct; if you were dealing with a tyro who was on the dead side and understood this to mean join downwind for a LH cct, that's a lot of holes in the cheese lined up.