I went with signing windows as my choice of guest book. I gotta say, it wasn't as cool as I thought it was going to be, but that was probably my fault.I am really big on having a guest book that you can use or hang after the wedding as a keepsake that can be forever seen. I ended up having two old windows and several colored sharpies. Let's just saw Sharpie's are not the best writing tool for window glass. Since I had two, each are equally bare and neither are full enough to justify hanging on a wall. But the idea was cute and the words people said were awesome.
So here are a few way cooler ideas than the one I chose. Ideas that could be used after the wedding in your home.
My favie fave is the shutter. If I did that, I would actually purchase the shutters and paint them awesome colors like the ones above. Those would make for some interesting art in your home by themselves but imagine having cute note cards popping out. Everything you looked at them, it would be a little surprise every time.