Voyeurmods.com Custom Etching Service Review
 

The final option is a 3-D laser etch. These are done with high precisions lasers that basically burn little dots on the window. It uses gray scaling techniques to give the impression that the image is 3 dimensional. There are only a few places that perform this level of etching. While they all have some stock images to choose from, the real fun stuff is when you take an image that you created or picked and have it etched on your window.

http://www.gruntville.com/reviews/misc/vm_window

Looks awesome :)