Step 4: The Feature
This is certainly the tricky and tedious part.
The holes on the plexi have to be squared off to accomodate the heads of the carriage bolts. The best way I found to do this was to use the Dremel tool with the 'multi-purpose' routing bit. Work a bit at each corner of each hole, and you should end up with an adequate square hole shortly. Test fit the bolt often, as it's always easier to take a bit more off than to put any back on.
Once the plexi is drilled and routed, spray both sides with the frosted spray paint. Use several coats, as the more frosted it is, the better it will diffuse the light.
On to the tedious... Print out a mirror image of whatever logo you want on the glass. Then, trace it onto your contact paper and cut it out with your exacto knife. Depending on how intricate a logo you choose, this could take a while...
Once the logo is cut out, stick it on the side of the plexi you want facing towards the back of the frame. This should look like a backwards picture of your logo. Proceed to put down several light coats of silver (or any reflective-colored) spray paint. I stress light coats here, because I ran into trouble with paint building up and running underneath my stencil. I then had to go and scrape out certain parts of the logo. This gave it a rough look which I kind of like, but could make a clean project real dirty, real quick. Another good idea (in hindsight) would be to mask off the front of the plexi, so it doesn't get any of the silver paint on it (which mine did). Let the paint dry thoroughly, and then remove the stencil. If all went well, you should have a nice logo on the backside of your plexi.