u/Apollo-Astra

I just randomly remembered this and wanted to know if anyone knows of it.

It's a picture book, not a novel, fairly light on text. It follows a creepy town where everyone has a diamond (or triangular?) symbol on their forehead, as well as on random buildings. I remember a water tower. The class was really engrossed in the story, we had theories about aliens and mind-control. I remember being disappointed that the truth is never revealed. So, picture book with diamonds on foreheads, that's the clue, but I can't find anything that matches it.

We're talking early 2000s here, def before 2010, I was in primary school.