I just was over at cockeyed.com, and wound up writing the following letter:
I was just reading your page about the crosswalk button sign that you made up, and I remembered something that I'd seen here (Yes, Walter Lewin is the man.) The effect is the same thing as a "halo" or "glory" generated by water droplets, so if you can simulate that, you can get reflective paint. Simple solution: wait until your latex paint is just tacky then throw sandblasting sand (little glass spheres) at it. Dry, and coat with a clear urethane coating. Viola! A wonderful reflective sign... and all for the cost of some sandblasting sand and urethane (which I'm certain you can find somewhere for less-than-cheap).
Best of luck in pulling off some awesome warning signs with this!
Hope someone can use this advice... eventually.
And eventually I'll put up pics. In the meantime, look at Lewin's end-of-term video about rainbows. It's amazing!