If it is not a secret i would like to ask you how are you doing these key caps? They look really nice!
Its not a secret, I just wanted to make one for myself then after It was completed I thought I'd show it here. I'll show you how I made it, It is quite the simple concept.
Ok first step is to find a bunch of random junk that would be cool and is small enough to fit on a keycap. ( No I did not make all of these I am not that awesome. The knights are some off-brand lego.)
Then you are going to want to grind off the back of whatever you picked at an angle, enough of one so its looking upward. You also need to get a keycap and grind it off so it is flat, don't grind too much off or there wont be anything left on the top, which obviously is not a good thing.
Then all you need to do is attach it onto the keycap using your favorite adhesive.
Then at this point, you can either leave it how it is, or use some paint and make it all one color, or give it a base coat and then paint it however you wish. Drop a clear coat on there if necessary, and there you go.