[Happy Color] why do the bats have letters tho

I'm not doing Every Single Halloween panel so I'm probably missing some, but: bats. with letters.

S O T H G spotted so far.

The pages are different styles, but there is a unifying theme.

I didn't even really spot the S and O for what they were when I was working, either!

(I could possibly solve this mystery by reading the News tab but what fun is that? XD)

oh good im not the only one using this app

I figured it out last night: GHOST