The Walking Dead was looking for a design to print on the back of some American Apparel jackets for the cast to wear in between takes.  A design company I was working for at the time asked me to mock something up with angel wings reminiscent of those found on Daryl's (character on the show) vest since they didn't have the original design. My guess is the vest worn on the show was just some found item that the wardrobe department decided to use, and not actually designed by anyone.