Board Thread:False Info and Speculative Discussion/@comment-25123326-20160216100917/@comment-26879545-20160219214649

Some people count 5a and 5b as separate seasons.

Also, like you said, the Oni went about marking any supernatural and pseudosupernatural (Lydia) creatures they could find in Beacon Hills while looking for the Nogitsune. If there was something about Danny that piqued their interest, they would have scanned him and given him the kanji. I just chalk that scene up to dramatic flair on the writer's part.