Wouldn't worry about it. I had all four tires once with that, and the dimples were spaced evenly apart, each 1/3 of the way around the tire.
It's a manufacturing issue, I think, or something done from the factory. At least, thats the way these Goodyears looked.
If it's only on one tire, and you're overly concerned about it, rotate that tire to the rear of the car. You'll have the peace of mind that IF it does blow, you'll still be able to steer to safety.