You know how your keyboard has little nubs on the j/f keys so its easy to find the home row without looking down? Reader pojken suggests doing something similar for your ever-present earbuds.
I make a simple knot in the cord as close to the left earpiece as possible. When I pick up the earpiece to put it in my ear or take a quick look at my earphone, I immediately know if it's left or right.
(BTW, I put the knot on the left side because when I was in bed, I'd lay on the right side of my face and didn't want the knot to hit my cheek.)
If knotting your headphone cords makes you a little wary (kinks in cords can be problematic for longevity), you could also just wrap some tape around the bud or something else along those lines. Sure, most earbuds come with the R/L identifiers printed on (I just bought a new pair that didn't, incidentally), but keyboards come with letters printed on them, too. That doesn't mean you want to look down every time you plop down at your computer.