Damage-Free Reusable Removable Standard Stikki Clip for Any Surface, White, Pack of 30 - 079044, 8-1/2 X 11 in

I think it would be easier (and look better) to get something like this, or any other 'note holder' that mounts with double sided tape. Edit: I'd actually recommend the type of clip where you can just slide the note in and pull it back out. The one I linked to, means people are going to be pushing on it and could accidentally break the doorbell. Something more along the lines of this: https://www.amazon.com/Stikkiworks-Damage-Free-Reusable-Removable-Standard/dp/B003U6OX40