I don't know if you are still looking for help on this but I use to install custom car audio and found Plexiglas quite fun for custom lighting and I think it may help you. If you light one edge of Plexiglas with a neon or LED all other edges will glow brightly. Anything etched in the smooth surface of the Plexiglas will glow as well.
One option could be to tape off the area you want to glow(the power symbol) on a piece of plexi about the size of the symbol and paint the rest black or whatever color(this is the front side). Etch (with a 400grit sand paper) the entire other side of the plexi(this is the back). Then use at least two (the more the brighter) LED's evenly spaced around the edge to light all etched space.
Another option would be to etch the actual symbol on the front and paint the entire back black or whatever color. This option looks really sweet
for two main reasons. One paint on the back side of plexi always looks smooth and shiny no matter how good (or bad) you are at painting. Two the symbol will appear to float above the painted surface. To etch the power symbol into the plexi you must tape of the entire area outside the symbol ( you can tape of the whole thing then cut out the symbol as well). Use a durable tape or double layer the tape. Next lightly sand the cut out area with a 400grit sand paper. Paint the entire back and light as stated before.
Best two practice a little first to get the hang of it but it really isn't that difficult and it looks really good. It may not end up as bright as your picture but depending on how many LED's you use and what color you use it can be pretty bright. Looks like a cool project though I wish you luck. Let us know how it is going. I want to see some pictures when your done. Post or PM if you need help.