I've not seen any ANSI symbol either, but I think what I would do would be to enclose an LED and a photo-transistor, or two totem-poled photo-transistors if you have a bi-polar output in a long box with the appropriate number of leads. That should indicate that these items are in one enclosure and also the proper connections to the cicuitry inside the enclosure. The box would, by default I think, be assumed to be retroreflective photo-eye as no other commonly used device fits that 'description'.