http://www.gideontech.com/guides/etching/
Basically what you do is use a dremel with various attachments and etch what you want into the lexan. You can put images behind the lexan to give you a guide if you want. People use it mostly for modding computer case windows on the side of their cases. Once done, you can paint it, or just let the etching do the work, although you wouldn't be able to see it from far away.
Just an idea