This one picked my brain for a while…
I never got shader maths working right and was wondering if there was another way to get retro reflective surfaces working in Blender.
And there is one! So simple in the end, just use a dense volume and turn down the anisotropy.
This works independent of the camera and works for every light ray in the scene, creating a very convincing effect. Love it! I must plaster them now around all of my scenes 
For showing how they work i created a quick night scene of driving down the road with the headlights on.
You can see how only the reflectors in the beam are bright, the others are almost invisible (i added a point light to the car to keep those also dimly lit).
The 60 second tutorial is here:
