I had an idea kicking around for a while for a large matrix screen made out of LED pixels. On top of pixels are clear plastic rods made out of Endlighten material.
This material is unique in that it's impregnated with microscopic metal particles that reflect and diffuse light, making the rods glow from light that enters either end.
I whipped up a quick Processing sketch to help me visualize such a sign in 3D. It's based on my previous work on the Domestar project - the data for the pixels comes from the domeTransmitter Processing sketch, and the results are displayed on a matrix of glowing tubes, arranges in a wave pattern.