I haven't seen a marking on the plug put there for the purpose of telling how to be inserted.

I did decide that I could overcome this problem, which is almost all it takes to overcome it. I noticed that all USB A connectors have a wide side without a seam and a wide side with a seam. So far, all manufacturers I've run across, including some really cheapass ones, put the seam on the same side. So all I have to do is learn which side the seam goes into on different devices.

My laptop, it's seam down. Car chargers, seam to the right. Except one, seam to the left. My Dell desktop, it's seam to the right. My previous Dell desktop, it was seam to the left.

Both of those desktops have the USB insignia above the socket, but it's pointed the same way on both computers even though the sockets are at 180 degrees to one another.

So, no, there's no marking. But it's not impossible to learn how to put them in for the devices you use the most. The biggest step in this process was deciding I could learn how to do it. (This is just like our clients who can only learn how to do something when they are given the confidence to believe that they can.)