I also have socks with side indicators. They're designed to fit the feet, so the entire socks are asymmetrical. Theoretically you could go by the pattern, but when you're pulling socks out of a hamper it's a lot easier to match them via letters which you know are always at the ends. It's pretty convenient and makes it impossible to match them incorrectly, so I think it's a good design choice.
I have 1 pair with similar indicators. The end of socks is not symmetrical, they are in a shape of foot to get a perfect fit and if you wear them the other way around they are not as comfortable. Good pair, I like them.