I'll shamelessly ride on the coat tails of Bob here and say that Ridge Street is another company that tests and observes directionality of cabling. With our offerings I don't so much hear specifically image height but an overall sense expanse to the sound stage. I also notice that the sound is less coherent if the cables are not oriented in the right direction. To make certain and as Bob mentions, with stranded wire, forget about it. With solid core, you do very well to pay attention if you're manufacturing cables and/or auditioning or testing cables.
In a very few instances, I wouldn't be surprised if some cable makers are just slapping arrows on to make their product more substantial looking. I've heard two occasions where the same product model sounded slightly different (one definitely better than the other) when the directional arrows were observed. Reversed both cables and the performance traded places!
In manufacturing and with the end user, it is expensive and time consuming to assure proper directionality but my ears say it's worth it.
