Those look just like sipes that are done at the tire store. I used to sipe tires when I worked at major tire retailer so I recognize them. When I used to perform siping, I would sipe perpendicular to the tire rotation direction(which is probably more commonly recognized). Depending on a variety of factors, siping can lead to chunks of the tire getting torn away as smaller pieces are cut from the siping. This is more common when siping tread with lots of factory sipes and siping that extends to the outer edges of the tire. Sipes in the center appear to be less vulnerable to damage and even more so, when they are not as deep.These tires were siped by the retailer, when they were first purchased. I requested that they be siped in the center only and at about 50% of the tread depth. The sipes were not very noticable when they were new, but became more obvious as the tires wore. Now the sipes are almost worn out of the tires and remain very shallow. as the tires wear, these will go away. Hope that helps.EDIT:Thanks to information in this thread, I have realized that though these cracks look very similar to siping, they are not caused by a retailer, and likely some sort of manufacturing related issue. These tires were replaced under warranty.