What do the secret switches look like in Grimrock 2?

I found this question very useful when playing Legend of Grimrock, because it shows the sort of detail to look out for without spoiling the actual locations. Are there images that show the different types in LoG2? Do they vary significantly between dungeons?

I'm pretty early in the game right now, and I've only seen a few obvious circular buttons and one that was an irregular brick corner. That irregular corner was nasty to find, and would have been much better if I knew what I was keeping an eye out for.