I asked layout artist Badger McInnes to play symbol-artist, but before Badger started, ASH LAW pointed me towards the treasure trove of Creative Commons symbols made available by @game-icons/. They're up to over 3300 symbols tailored for gaming, wonderful stuff for both published games and prototypes.
The site is searchable with tags and it was no problem to find ten symbols that worked by Lorc and Delapouite. Badger slightly modified the symbols, we handled the Creative Commons licensing text in the credits, and you can find them on page 103 of Book of Demons. Here's a snippet of the page with Gareth's text and three of the symbols . . . .
My stupid mistake was that I miscounted and only credited them with nine symbols. I left the Cultist icon by Lorc out of my count, the symbol just above. We ended up using ten symbols from game-icons, not nine. I didn't discover the error until I was writing this blog post and realized I wasn't going to be able to simply recommend the game-icons site, I also need to apologize for screwing up the count.
Recommendation: Game-icons is a wonderfully useful site. Follow them on twitter at @gameicons. Design a game about prehistory because they just uploaded wonderful prehistoric icons. Have fun!