Hole in road bike tire This is 700x25 continental Ultra Sport II

I noticed there are two holes in both tires, and wonder if this is a manufacturing fault, or simply a wear indicator?
Yes, those are wear indicators.

The change is noted by retailers:


  Note: Continental has added wear indicators to all Continental
  Gatorskin tires. These small divots in the tread surface are
  intentional and are not a sign of a factory defect. Once the rubber
  wears to the point where the divots are no longer discernible, you'll
  know it's time to replace.