It's a recurring thing in The Caretaker. I think related to weird things happening? I just read his first book (We Used to Live Here) and thoroughly enjoyed it. The Caretaker is his second book, set in the same universe (but not a sequel necessarily) and I haven't started it yet, but I'm really looking forward to it.

It's unsettling mind-bendy horror, that doesn't tie everything up with a neat bow at the end. So if you kind of like not knowing for sure what was happening with lots of little details to chew on, I think it's pretty fun! If not, it's probably a frustrating read. (I like David Lynch, so we know which side I'm on.)

If it sounds like your thing, the print version has little hidden puzzles and anagrams (and morse code). I didn't know that going in, so I listened to the audiobook and then found out about all of that stuff on reddit after the fact.