A Killer Among Us in paper

I've been playing a lot of [[A Killer Among Us]] and arena makes it easy to denote your secret choice. However, I haven't played with or against the card in my paper prereleases or drafts. I plan on playing quite a bit of limited this weekend at MagicCon and was wondering what would be the best way to choose a secret creature type for this card.

Do I just rip off a piece of my life pad and write it down? Do I need to call a judge in comp REL?

I'm relatively new to the game so I'm not sure if there is a precedent with cards like this.

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