Hi Benny,
You can adjust transparency of Invigorator layers to reveal layers behind them. (Where you texture your models click the transparency box and adjust to taste... to get fancy, add a transparency map.) That should get you started.
If you're trying to get it to look like an actual light source is inside or behind the sign, try adding one of the lighting filters out there - fe lightburst or the new one, "shine" from trapcode.com. BTW, it's just been released and is on special for $50. ...
http://www.trapcode.com.
For what it's worth, I'd recommending pre-rendering the sign elements with Invig (save your movie as millions plus alpha channel/animation codec), then applying lighting and other filters to the resulting movie. You'll save rendering time in the long run.
If you give us a little more specific description of your project, we can provide some more specific answers.
Hope this helps... have fun!
Jon