I don't know how to create spoiler tags So the question below has spoilers!
So entry 220 says that you have to mark the site as the temple of the skull, do you write that down or is there a sticker for it? There's a suspicious looking skull symbol sticker on the explore sheet but it's not explocitly stated that this is what is used to mark it.
yes, that's what it is.
To use a spoiler, click the button that says "SP" above the text box. It's to the right of the dropdown menu that says "Insert Geek Link"