“Gareth drew a big red A just like that on the church.”
You may be on to something. (I have not read the comics, so I dunno if that is in there or not)
Remember that one of the previous episodes, I think it was the first split of the previous season, when the group first showed up at Terminus, was named “A”. When they Terminus people were herding the group toward the railroad car, one of the buildings they herded them into was marked “A”.