My grandmother used to keep brightly-colored glass objects on her windowsills. I thought this collection, like so many of her other ones, was just an expression of her eccentricity. Mom filled me in on a little secret the glass was pretty, yes, but also an effective security device before the advent of alarm systems.
The windowsill is an obvious place to locate things that need light, like plants. But I've discovered that people collect all sorts of kooky things for display on their sills. What do you have on yours?