To be fair, I tend to LIKE the "this symbol means this" universal concept. The "box with arrows in all directions" seems to be a universally-understandable concept for a turbolift. I don't see any reason why you need to omit an arrow if you're on the top floor, bottom floor, or have an inpenetrable wall to one side or another... or, for that matter, why there doesn't seem to be a "depth arrow" in the diagram (surely lift cars occasionally travel normal to the door opening, don't they?) Certain symbols are well-understood, just by virtue of the symbol. The intention, as I understand it, with TMP's graphics (which I DO think were overdone a bit) was to create a 23rd-century version of the "Drivers manual" symbol recognition chart. The "lift car with arrows in horizontal and vertical directions" strikes me as very much that sort of thing.