Okay, you know I'm a science fiction writer, right? So "Signs" automatically made me think of crop circles (strangely, I've never seen the movie by the same name). Crop circles are rather close to my heart as one of my early published stories centered around them. Even if they're all hoaxes, they're cool to look at. And if they're not all hoaxes...
Anyway, this is based on a crop circle that appeared in Wisconsin. It's ACEO size, Prismacolors on Somerset Velvet Newsprint Grey.