It might mean they need more calcium. My hens laid a few like that so we went to the feed store and a very helpful young man told us to try adding oyster shell to their feed or just getting a new feed with some already mixed in. Within a week no more wrinkled eggs and the shells are thicker and my hens look healthier now too. Good luck with the eggs!
Here's a link to my favorite egg quality page. It addresses the problem you are having. It's not anything to worry about, just aesthetically displeasing. It happens in my older hens fairly often these days.