There are many symbolic elements within TWDU, and JSS is just one that proved vital to the survival of one character.
Throughout the eleven-season run of AMC's apocalyptic series The Walking Dead, there have been many elements that proved to be symbolic in the character's lives. Rick's hat (Andrew Lincoln), Glenn's (Steven Yeun) pocketwatch, and more come to mind. During season six of the series, three letters are a mantra that keeps this character alive.
Ep. 602, "JSS," featured an attack on Alexandria by the Wolves and a flashback story of Enid (Katelyn Nacon), who was introduced in the previous episode. Enid appeared at the gates of Alexandria, and although she was leery of the residents, she was welcomed.
The flashback scenes reveal that Enid's parents were devoured by walkers right before her eyes. After their deaths, she wandered about the wilderness, alone where she was seen writing JSS on windows, her arm, and other spots. This seemed to be something that soothed her, a mantra that helped her survive. Before entering the gates of Alexandria, she almost walked away but glanced down at the JSS on her arm and changed her mind.

During the Wolves attack on the community, Enid tells Carl she is going to leave Alexandria as it iis too large to protect. Despite Carl's pleas for her to stay she is determined to leave. He asks her not to say goodbye. She keeps her promise with a note which reads, "Just survive somehow."
Eventually she encounters Glenn and returns to the community with him. Sadly, Enid's mantra doesn't save her from the harsh world of the apocalypse. In episode 915, "The Calm Before," Enid would become a member of Alpha's (Samantha Morton) pikes.
Enid was portrayed by actress Katelyn Nacon who recently starred in several movies, Familiar Touch, Southern Gospel, Devil's Peak, Breathing Happy, and Linoleum.