I was watching HTTYD 1 when I saw this:

Look at the 'h' in night. Look familiar?

It looks almost exactly like what Gothi put on Hiccup'a forehead when he became chief. Ok, the theory. I believe Gothi put an 'h' on Hiccup's forehead to symbolize his name. In my opinion, the added arc means a higher power, like chief.

Just a little theory I thought up. Hope you enjoyed!