Early in the series, Norman Reedus' character Daryl Dixon rode a motorcycle but lost it over the course of the series' tumultuous stories. When talking with producers about future stories, he said that he wanted to be on a bike again, and they agreed.
Reedus suggested Classified Moto to the producers because the company had already built a custom cycle for him. The builders there came up with a pair of custom Hondas that are made to look beat-up and utilitarian in the show's post-apocalyptic world. There's even a mounting point on the back for Daryl's trademark crossbow.
The bikes also had to be reliable in the real world for filming. According to Classified Moto, it chose the Hondas as a base because the company had experience building customs on them and parts were easy to get.
While Classified Moto now gets its bikes on TV this week, this isn't its first brush with celebrity. The company previously built Battlestar Galactica star Katee Sackhoff a highly modified Honda, as well.