Seems like the industrial designers at Motorola Mobility found a solution to this. At least I found it to be pretty effective myself. The body of the jack is curved down in the middle ever so slightly to naturally match the curve of your thumb as you hold it, this gives you a good feel of the orientation of the jack just by holding it without even looking at it.
Yes other mobile companies, including Apple before they came up with the bi-directional jack, did provide a small etched marking on the top side of the jack to indicate that it had to face that way. But neither our fingers are sensitive enough to feel the mark when we are not looking at it, nor our eyes are good enough to see it in the dark.
Some of you may argue that Apple provides the best solution with its bi-directional jack, which can be plugged in either way. Well, no doubt about it. It’s actually an inspired piece of engineering. But then how many of us would wish to trade the use of that jack with our freedom to use other devices as well as our own older devices adapters to charge or to transfer files? Oh heck, forget other devices, I now have to carry two cables for my two Apple devices, one for the older iPod and one for my iPad Mini! So till the day Apple is generous enough (trust me that day will never come) to open their bi-directional jack technology to all, I feel Motorola’s simple little tweak in the adapter design will remain as the most usable and cost-effective solution.